Excessive maternal weight and pregnancy outcome

Excessive maternal weight and pregnancy outcome John

w.e. Johnson, MD, Jeffrey A. Longmate, PhD, and Barbara Frentzen, RN, MSN

Gain esville, Florida OBJECTIVES: This study was undertaken to determine the influences of increased maternal prepregnancy weight and increased gestational weight gain on pregnancy outcome . STUDY DESIGN: This was a longitudinal retrospective study of 7407 term pregnancies delivered from 1987 through 1989. After excluding cases with multiple fetuses, stillbirths, fetal anomalies , no prenatal care, selected medical and surgical complications, and those with incomplete medical records, 3191 cases remained for analyses by determination of odds ratios for obstetric outcomes, by x2 tests for significant differences and by adjustment for risk factors with stepwise logistic regression. RESULTS: Both increased maternal prepregnancy weight (body mass index) and increased maternal gestational weight gain were associated with increased risks of fetal macrosomia (p < 0.0001), labor abnormalities (p < 0.0001), postdatism (p = 0.002), meconium staining (p < 0.001), and unscheduled cesarean sections (p < 0.0001) . They were also associated with decreased frequencies of low birth weight (p < 0.001). The magnitude of the last was less than that of the other outcomes . CONCLUSIONS: Increased maternal weight gain in pregnancy results in higher frequencies of fetal macrosomia, which in tum lead to increased rates of cesarean section and other major maternal and fetal complications. Because these costs of increased maternal weight gain appear 10 outweigh benefits , weight gain recommendations for pregnancy warrant careful review. (AM J OeSTET GVNECOL 1992;167:353-72.)

Key words: Pregnancy, body mass index, weight gain, cesarean section In recent year s there has been much interest in the association between poor maternal weight gain and low birth weight (LBW) .'·4 Because of these observations, recommendations have re cently been made by the National Academy of Science to ad vise further weight gain increases during pregnancy.' These recommendations have been made on the basis of several assumptions: (1) The morbidity and mortality associated with LBW is due in part to poor maternal nutrition, as reflected by low gestational weight gain. (2) Through nutritional counseling and support, maternal gestational weight gain can be increased. (3) Increasing gestational weight gain will eliminate or reduce the frequency of LBW complications. Unfortunately, these assumptions have not been evaluated by carefully designed, recent studies in a United States sample. However, on the basis of these assumptions there have been frequent articles in the lay press encouraging pregnant patients to eat "to appetite.:": ? Publications dealing with prepregnancy counseling and preparation for pregnancy give limited attention to the potential complications of excessive maternal prepregnancy weight and excessive gain during pregnancy.

From the Departments of Obstetricsand Gynecology, College of Medicine, and Department of Statistics, University of Florida. Presented at the Fiftyfourth Annual Meeting of The South Atlantic Association of Obstetricians and Gynecologists, Palm Beach,Florida, January 26-29, 1992. Reprint requests: John W.C. Johnson, MD, Box 100294, University of Florida College of Medicine, Gainesville, FL 32610. 6161)8060

These considerations are of great interest to clinicians , because of an increasing percentage of obesity among pregnant patients' and because of the greater cesarean section and complication rates observed among such patients. Accordingly, this study was undertaken to assess the adverse effects of excessive maternal weight on pregnancy outcome. There have been a number of other studies addressing these issues. B·" This analysis is different in that it focuses on a recently delivered population of women, the majority of whom received nutrition counseling and the benefits of modern obstetric, anesthetic, and pediatric care. It therefore reflects current improvements in care. It also explores the influence of prepregnancy status (body mass index) as defined and categorized in the recent National Academy of Sciences publication>and weight gain during pregnancy, in conjunction with other important risk factors.

Methods With a computerized data system for all deliveries at our institution from Jan. 1, 1987, through Dec. 31, 1989, we identified a total of 7407 patients delivered at or beyond 38 weeks of gestation. The study group consisted predominantly of patients who received care from the prenatal clinics of the University of Florida, Departments of Obstetrics and Gynecology. These clinics serve a twelve-county section of North Central Florida that includes a college town but is otherwise predominantly rural. Three to four percent were private patients. The majority of the remaining patients were

353

354 Johnson, Longmate, and Frentzen

of low-income status (::S 150% of federal poverty level). All patients were counseled by a nutritionist and encouraged to gain ~24 pounds. No limit was placed on maximum weight gain. Glucose screening was routinely done for diabetes mellitus on all patients at 24 to 28 weeks' gestation. Information on each patient was entered on standardized forms at the first antepartal visit, at delivery, and at discharge from the hospital. After verification for accuracy, the nearly 200 variables were computerized. All singleton pregnancies delivered at ~38 weeks that received prenatal care and were delivered of live infants in Shands Hospital were included in this study, provided they were not diagnosed with fetal abnormalities, oligohydramnios, or polyhydramnios. There were 6634 patients meeting these criteria. Another 1463 patients with identified relevant medical or surgical complications (gastrointestinal disorders, sickle cell hemoglobinopathy, hepatitis, hematologic disorders, malignant disease, renal disease, neurologic disease, pulmonary disease, psychiatric disorders, tuberculosis) were excluded. Patients with appendicitis, nonhemoglobinopathic anemia (hematocrit <30%), bone or joint disease, urinary tract infections, and asthma were retained because their exclusion would have significantly reduced the total numbers and because these complications did not appear to influence the outcomes of interest. For purposes of this study, we grouped all patients together who voluntarily admitted to tobacco, alcohol, or illicit drug use as patients admitting to substance abuse. Patients with the diagnoses of diabetes, preeclampsia, and chronic hypertension were included for special studies as noted. Seven hundred four cases were excluded because of incomplete risk variable data; an additional 1276 cases were excluded because of incomplete outcome variable information. The final number of deliveries left for analyses was 3191. The mean sociodemographic characteristics (maternal age, parity, level of education, ethnic group proportions, percentage receiving private medical care, number of prenatal visits, and gestational age) and the mean anthropometric features (maternal height, body mass index, gestational weight gain, net weight gain, and infant birth weights) for the entire sample were not significantly different from the study sample (p > 0.05). Pregravid weight was determined on the basis of maternal reporting. The weight recorded at the last prenatal visit was designated as the maternal weight at delivery. The mean length of time between last prenatal visit and delivery was 6.1 ± 6 days. Weight gain during pregnancy was calculated by subtracting the self-reported prepregnancy weight from the maternal weight last recorded before delivery. Height was measured and recorded on registration. Birth weight was measured and recorded at delivery.

August 1992

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Gestational age was assigned by the physician delivering the patient on the basis of the best estimate from menstrual data, physical examination, and ultrasonographic studies. Race, marital status, private or nonprivate care, educational level, and parity were all obtained from the prenatal history. Information concerning drug abuse was voluntarily provided by the patients during routine questioning, usually on the first prenatal visit. Intrapartum complications were recorded by the physicians delivering the patients, including the presence or absence of fetal heart rate (FHR) abnormalities, labor abnormalities, and meconium staining. Fetal gender, birth weight, Apgar scores, and the presence or absence of neonatal resuscitation were derived from delivery room data. We chose to evaluate the relationships between certain outcomes and the following risk factors: (1) prepregnancy weight stratified into quartiles; (2) height «62 inches, 62 to 65 inches, and >65 inches); (3) body mass index stratified into the four groupings recommended by the National Academy of Sciences"; (4) maternal gestational weight gain stratified into quartiles for this patient population, into quartiles of net gestational weight gain (total maternal weight gain minus baby's birth weight), or according to National Academy of Science recommendations for body mass index, as being below, within, or above the recommended range" (patients with obese body mass indexes 'were assigned a recommended range of 15 to 25 pounds); (5) ethnic groups (white, black, and other); (6) gestational age 38 to 42 and >42 weeks; (7) married or single; (8) private physician care or not; (9) education (less than high school graduate, high school graduate, and any beyond high school graduation); (10) parous or not; (II) maternal age «20, 20 to 26, and >26 years); (12) admitted smoking, alcohol, or illicit drug use; (13) fetal gender; (14) birth weight categorized into <2500 gm, 2500 to 4000 gm, and ~4000 gm; (15) maternal diabetes (pregestational and gestational) or not; and (16) hypertensive or not. Outcome variables studied included (1) fetal macrosomia (~4000 gm) and (2) low birth weight «2500 gm) where the risk factor birth weight «2500 gm, 2500 to 4000 gm, and >4000 gm) was excluded. The risk factor of birth weight was included in assessing the following outcomes: (3) meconium staining, (4) I-minute Apgar scores, (5) 5-minute Apgar scores, (6) unscheduled cesarean sections, (7) oxytocin induction, (8) oxytocin augmentation, (9) labor abnormality (prolonged latent phase, protracted active phase, secondary arrest of dilation, arrest of descent, prolonged second stage), (10) FHR abnormality (decreased variability, bradycardia, or tachycardia for> 10 minutes, multiple variables, or late decelerations), (II) cord umbilical artery pH <7.12, (12) newborn resuscitation (artificial ventilation

Increased maternal weight and pregnancy outcome 355

Volume 16 7 Number 2

Table I. Study population characteristics by body mass index group Body mass index category

Characteristic

Prepregnancy weight quartile (lb) 1 (:511 6) 2(11 7-132) 3 (133-155) 4 (> 155) Height (in) 1 «62) 2 (62-65) 3 (>65) Weight gain (lb) 1 «1 6) 2 (16-25) 3 (26-35) 4 (>35) Net weight gain (lb) 1 « 14.9) 2 (14.9-23.5) 3 (24-33.0) 4 (>33 .0) Weight gain, National Academy of Science Low Within range Over Ethnic group White Black Other Private physician No Yes Married No Yes Tobacco, alcohol, dru gs No Yes Parity First Multiparous Male infant No Yes Maternal age (yr) < 20 20-26 >26 Maternal education < 12th grade 12th grade > 12th grade Hypertension Yes No Diabetes Yes No Birth weight (gm) <2500 2500-4000 > 4000 Gestational age ~42 wk No Yes

Low « 19.8) (n = 755)

Medium

High

(19.8-26) (n = 1621)

(2 7-29) (n = 329)

Obese (>29) (n = 486)

All

(n

= 3 191)

582 161 12 0

228 644 654 95

0 5 105 2 19

0 0 24 462

810 810 795 776

89 363 303

220 859 542

54 160 11 5

88 257 141

451 1639 11 01

59 140 265 291

190 292 467 672

65 63 93 108

157 107 84 138

471 602 909 1209

133 207 229 186

341 409 404 467

101 80 85 63

221 102 83 80

796 798 801 796

254 317 184

431 518 672

49 79 201

137 127 222

871 1041 1279

487 254 14

972 615 34

164 161 4

252 231 3

1875 1261 55

734 21

1555 66

317 12

476 10

3082 109

433 322

874 747

196 133

246 240

1749 1442

455 300

1042 579

230 99

341 145

2068 1123

372 383

698 923

123 206

151 335

1344 1847

381 374

812 809

166 163

239 247

1598 1593

276 338 141

500 754 367

85 161 83

80 262 144

941 1515 735

390 285 80

729 676 216

135 156 38

177 237 72

1431 1354 406

26 729

74 1547

19 310

52 434

171 3020

14 741

38 1583

20 309

26 460

98 3093

36 673 46

32 1381 208

273 51

5

1 401 84

74 2728 389

694 61

1476 157

289 40

430 56

2877 314

356 Johnson, Longmate, and Frentzen

20

August 1992 Am J Obs tet Gynecol

-0- Low Birth Weight -.- Macrosomia

-/:r Cesarean Section

15

w

~ ~ zw 0

10

a: w

a..

5 p
26-29

19.8-26

<19 .8

>29

MATERNAL BMI Fig. 1. T his graph of unadjusted data shows th e r elationship between increasing maternal bod y mass index (BMI) and frequencies of macrosomia, cesarea n section , and LBW. There is a very similar rise in both macrosomia and cesarean section rates with increasing maternal body mass index. p Values re present statistical significance between successive ra tes of cesarean section . Decrease in percentage of LBW (of lesser magnitude) is also noted with increasing maternal bod y mass index.

20 -0- Low Birth Weight -.- Macrosomia

-/:r Cesarean Section

15 w

~

~

o

10

p
a: w

a.. 5 pcO.1

OL..--'------........JL.-------'----_ _---' <16

16-25

26-35

>35

GESTATIONAL WEIGHT GAIN LBS Fig. 2. T his graph illustrates unadjuste d relationships between increasing maternal gestatio nal weight gain and freque ncies of macrosomia, cesarean section , and LBW. As in Fig. I , there is almost identical alteration in frequencies of macrosomia and cesarean section with increasing gesta tional weight gain . p Values re present statistical significance for d ifferences between successive ra tes of cesarean section . T he re is corresponding decrease in LBW of lesser magn itude, also noted with risin g gestational weight gain .

and endotrachea l int ubation), (13) shoulder dystocia, and (14) postdates (gestational age excluded as a risk factor ). Patients with the diagno sis of preeclampsia (includ ing pregnancy-induced hyperte nsion , preeclampsia mild or severe, and eclamps ia) and chronic hyper-

ten sion (with or without superim posed preeclamps ia) were included in assessing the associations between ris k factors and the occurren ce of th ese spe cific complications. For the statistical evalu ations , all risk factors were

Increased maternal weight and pregnancy outcome

Volum e 167 Number 2

8MI = Low

357

8M! = Medium

~

~

r~

r'

S~

i3:

• € "0 3:

.. ~ €

I·

~

13.8~

~ -21)

21)

'"

60

W"'V'lIGain(bs)

..

11. 4 ~

~

p..O.OOOl 100

p..O.OOOl .21)

20 W_ _ .. 11ls1

8MI - High

60

100

8MI = Obese

~

-3::~ . ~~ 6.4~

~

..

P.0 .0001 .21)

20

'"

WflightGain (Ibs)

60

100

·20

20

.. 1Ils1 w_ _

60

.

100

Fig. 3. This scatte rgram gr aph depicts unadjusted relationship between weight gain and birth weight in the four bod y mass ind ex (BM!) categories. Substantial variation in birth weigh t is readily seen. There is significant reduction in association of weight gain to birth weight as bod y mass index increases, but association even among obese patients is stat istically significant (p < 0.000 1).

d ivided into intervals as described above, with odds ratios used to describe the effect of each level of a risk factor, relative to a reference gr oup. The significance of each unadjusted odds ratio was assessed with a X2 test. Stepwise logistic regression was used to select an adj ustment model, and th e adjusted odds ratios were derived from the anti-logs of parameters estimated by logistic regression. The Wald X2 statistic provided a significan ce level for each adjusted odds ratio, and confiden ce intervals for odds ratios were formed by transforming the estimates, give or take two standard errors, from the log odds scale. Weight gain , prepregnanc y weight, and height were included in each adjustment model , regardless of statistical significance. In the trend anal yses all risk factors were examined, but only those selected by a stepwise procedure at the 0.01 level of significance were included in the model. Net weight gain was used when examining birth weight and the incidences of macros omia and low birth weight. The magnitudes of the tr ends in risk of an outcome were expressed as odds ratio for either a IO pound difference in weight gain, or a five unit difference in body mass ind ex, because these were round numbers

near the average width of the intervals used in the National Academy of Science categories and recommendations. This research proj ect was approved by the Un iversity of Florida Health Center Institutional Review Board. Results

The characteristics of our study population are tabulated in Table I. There were 3191 total patients in the study, including 171 with th e diagnosis of hypertension (includ ing preeclampsia) and 98 with the diagnosis of diabetes. According to bod y mass index category, 24% were below normal, 51 % were within normal range, 10% were abo ve average, and 15% were obese. About 58% of the patients were white , 40 % were black, and 1.7% were Hispanic or Oriental. Overall , 55% were unmarried and 42 % wer e nulliparous. High school graduation or education beyond high school may be used as a measure of moderate to high socioeconomic status . About 55% achi eved these levels of education. Private physician care was used by 3.7% of all patients. The prevalence of admitted substance abuse (smoking, alcohol, or illicit d rugs) was 35 %.

358 Johnson, Longmate, and Frentzen

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Table II. Fetal macrosomia

Prepregnancy weight quartile (lb) 1*(5116) 2 (117-132) 3 (133-155) 4 (> 155) Height (in) 1* «62) 2 (62-65) 3 (>65) Body mass index category, National Academ y of Science Low* « 19.8) Medium (19.8-26) High (27-29) Obese (>29) Net weight gain (Ib) 1* (14.9) 2 (14.9-23.5) 3 (24-33) 4 (>33) Ethnic group White* Black Oth er Gestational age 2:42 wk No* Yes Married No* Yes Tobacco, alcohol, drugs No* Yes First birth Yes* No Fetal sex male No* Yes Maternal age (yr) < 20 20-26* > 26 Education < 12th Grade 12th Grade* > 12th Grade Diabetes No* Yes

Adjusted odds ratio and 95% confi dence mt erual

Odds ratio and 95 % confidence uu eroal

Characteristic

p Valu e

5.8 11.7 11.8 19.7

2.16 (1.5-3.1) 2.18 (1.5-3.1) 3.99 (2.8-5.6)

0.0001 0.0001 0.0001

NS NS 3.55 (2.64-4.78)

0.0001

5.5 12.1 15.1

2.3 (1.5-3.6) 3.0 (1.9-4.7)

0.0001 0.0001

1.9 (1.2-3.1) 2.2 (1.3-3.6)

0.53 0.11

6.1 12.8 15.5 17.3

2.27 (1.6-3.2) 2.83 (1.8-4.3) 3.22 (2.2-4.7)

0.0001 0.0001 0.0001

1.82 (1.38-2.4)

0.0001 0.44 0.97

8.5 8.9 12.6 18.7

1.05 (0.74-1.48) 1.54 (1.12-2.14) 2.46 (1.8-3.3)

0.8 0.008 0.0001

1.2 (0.83-1.75) 1.77 (1.24-2.52) 2.86 (2.02-4.02)

0.32 0.0012 0.0001

15.5 7.4 9.1

0.43 (0.34-0.55) 0.54 (0.22-1.38)

0.0001 0.19

0.36 (0.27-0.47) NS

0.0001

11.2 21.0

2.1 (1.6-2.8)

0.0001

1.9 (1.4-2.6)

0.0001

11.2 15.6

1.8 (1.4-2.2)

0.0001

13.9 9.0

0.61 (0.48-0.78)

0.0001

0.5 (0.39-0.66)

0.0001

9.7 14.0

1.5 (1.2-1.88)

0.0001

1.75 (1.37-2.24)

0.0001

9.3 15.1

1.7 (1.4-2.1)

0.0001

1.76 (1.4-2.23)

0.0001

8.8 12.7 15.4

0.66 (0.5-0.87)

0.003

0.48

1.24 (0.97-1.6)

0.087

0.75

10.6 11.8 19.0

0.89 (0.7-1.12)

0.318

0.88

1.75 (1.29-2.35)

0.0001

1.6 (1.18-2.16)

0.0018

2.15 (1.32-3.5)

0.002

1.75 (1.03-2.97)

0.035

11.9 22.4

0.68

NS , Not significant. Overall incidence 12.2%.

*Refer ence group. In this population the frequencies of fetal macrosomia and unscheduled cesarean section appear to ri se almost sim u ltan eou sly in r elationship to inc r easin g maternal body mass index ( Fig . 1) and to increasing gestational weight gain ( Fig. 2). As both body mass index and gestational weight gain rise, the incidences of macrosomia and cesarean section increase to involve one of six patients (8.9% to 14% or 15%, p < 0.001), whereas the LBW r ate declines (4% to 1 P < 0.00 1).

s;

Birth weight. The unadjusted data displayed a strong association between gestational weight gain and birth weight within the four body mass index groups ( Fig . 3) . This association was less among women with higher body mass index but still very significant (P = 0.000 I). A multiple r egr essio n of birth weight on net weight gain, body mass index, and se ven covariables selected by stepwise fining revealed an increase of 15.4 ± 2.2 gm birth we ight per pound gained by the mo th er (P < 0.0001) and an in crease of 66.9 ± 95 gm

Volume 167 Number 2

Increased maternal weight and pregnancy outcome 359

FETAL MACROSOMIA=12.2% BMIMID BMI HI BMIOB NET WT. GAIN 2 NETWT. GAIN 3

p
NETWT. GAIN 4

0.5

1

2

5

Odds Ratio Fig. 4. This graph depicts stepwise increase in un adjusted odds ratios for fetal macrosomia with increasing maternal body mass index and increasing net gestational weight gain. Adju sted trends test was significant at p < 0.001. BMf, Body mass index; DB, obese.

per unit body mass index (p < 0.0001). Height, race (black vs white), postdate delivery, substance abuse, fetal gender, parity, and diabetes were all associated with birth weight change (p < 0.0006). The effect of body mass index appeared to be nonlinear, leveling off at higher values , but no curvature was detectable in the association with weight gain , adjusting for covariables. Age, education, marital status, private ph ysician, and hypertension did not appear related to birth weight (p ~ 0.01). Macrosomia and low birth weight. The overall incidence of fetal macrosomia, defined as a birth weight of ~4000 gm, was 12.2% for this study population Crable II). The frequency of macrosomia increased in association with increasing prepregnancy weight, maternal height, maternal body mass index, and net gestational weight gain. Both body mass index and net weight gain demonstrated significant odds ratios for macrosomia (Fig. 4). After adjusting for risk factors by stepwise logistic regression, the model still exhibited significantly increased ratios for the highest prepregnancy weight group, the medium body mass index group, and increasing net weight gain. The lack of a statistically significant adjusted odds ratio for high or obese body mass index categories may be due to the smaller numbers in these categories and associations with confounding risk factors. The adjusted odds ratios also were significantly elevated for postdatism, parous patients, patients with higher education, those delivering male infants, and diabetics. Patients admitting to substance abuse and black patients were at reduced risk. After adjusting maternal height and age, marital status, and hyperten-

sian did not exhibit significantly altered odds ratios for macrosomia (Fig. 5). The trends analysis done by stepwise logistic regression revealed increasing risk of macrosomia with both increasing weight gain (odds ratio 1.3 for a 10-pound difference, p = 0.0001) and with increasing body mass index (odds ratio 1.5 for a 5-unit difference, p = 0.0001), adjusting for height, race, education, substance abuse, fetal gender, parity, and postdate delivery. (No interactions or nonlinearity involving weight gain and body mass index were detected.) The frequency of diagnosed shoulder dystocia was 1.8%. There was a trend to increasing odds ratio noted with increasing maternal gestational weight gain, but after adjusting for the listed risk factors only macrosomia was significantly associated with an increased odds ratio: 5.3 (3.0-9.3; P < 0.0001) compared with infants weighing 2500 to 4000 gm . Defining LBW as < 2500 gm , we noted an overall incidence of 2.3 % in this term population (Table Ill) . Maternal prepregnancy weight, maternal body mass index, and net gestational weight gain related inversely to the risk of LBW (Fig. 6). Male fetuses had a significantl y lower odds ratio for LBW. Patients admitting to substance abuse had a higher risk of LBW. After adjusting for these risk factors, high maternal prepregnancy weight, higher net weight gain, multiparity, and delivering a male infant were associated with low odds ratios for LBW. Patients admitting to drug abuse and black patients demonstrated increased odds ratios. The trends analysis of LBW demonstrated an estimated odds ratio of 1.4 (P = 0.0007) associated with a

360 Johnson, Longmate, and Frentzen

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FETAL MACROSOMIA=12.2% PRE PREG.>155 WT. GAIN 2 WT. GAIN 3 WT. GAIN 4 BMI MED. G.A.~42

WKS

PAROUS HIGHER ED. MALE FETUS DIABETES DRUGS BLACK

0.2

0.5

2

5

Odds Ratio Fig. 5. This graph illustrates odds ratios and 95% confidence intervals for fetal macrosomia for variety of risk factors, after adjustment by stepwise logistic regression. Number of obstetric and demographic characteristics were associated with increased fetal macrosomia. Black patients and patients admitting to substance abuse (drugs) were noted to have significantly reduced frequencies of fetal macrosomia. BMI, Body mass index.

lO-pound difference in weight gain, and an odds ratio of almost 3 (P = 0.0001) associated with a 5-unit difference in body mass index. Unscheduled cesarean section. In analyzing the frequency of cesarean section, we chose to exclude all electively scheduled cesarean sections and analyzed only those occurring because of complications during labor. The overall incidence for this study population was 11.9% (Table IV). A significant increase in the odds ratio for cesarean section was noted with the higher body mass index categories, the higher prepregnancy weight categories, and the greater gestational weight gain categories. Macrosomia, nulliparity, higher education, diabetes, hypertension, and private care were also associated with increased odds ratios for cesarean section. Adjusting for risk factors yielded significantly increased odds ratios for the highest gestational weight gain group, private care, nulliparity, and fetal macrosomia. Being a teenager and being tall were both associated with reduced odds ratios for unscheduled cesarean section (Fig. 7). Maternal race, substance abuse, and fetal gender did not appear to

influence this rate. The trends analysis done by stepwise logistic regression demonstrated an increased risk of unscheduled cesarean section associated with increasing birth weight (p < 0.0001), maternal gestational weight gain (p < 0.0001), and body mass index (p < 0.0001). Postdates. The overall frequency for postdate pregnancies in this study population was 9.8% (Table V). Increased odds ratios were noted with higher maternal prepregnancy weight, higher gestational weight gain, white patients, fetal macrosomia, and admitted substance abuse. After adjusting for these various risk factors, the odds ratios were significantly elevated only for higher prepregnancy weight, patients admitting to substance abuse, and patients with fetal macrosomia. Older patients and black patients had reduced odds ratios. There was evidence on trends analysis that risk increased with weight gain (odds ratio 1.13 for a lO-lb difference, p = 0.0014) and with body mass index (odds ratio 1.2 for a 5-unit difference, p = 0.0003). Labor abnormalities. The overall frequency of labor

Increased maternal weight and pregnancy outcome 361

Volume 167 Number 2

Table III. LBW Odds ratio and 95% confidence interoal

Characteristic

Prepregnancy weight quartile (Ib) 1* (:5116) 2 (117-132) 3 (133-155) 4 (>155) Height (in) 1 «62) 2 (62-65) 3 (>65) Body mass index category, National Academy of Science Low* «19.8) Medium (19.8-26) High (27-29) Obese (>29) Net weight gain (lb) 1* «14.9) 2 (14.9-23.5) 3 (24-33) 4 (>33) Ethnic group White* Black Other Married No* Yes Tobacco, alcohol, drugs No* Yes Parity 1* >1 Fetal sex male No* Yes

Adjusted odds ratio and 95% confidence internal

p Value

0.24 (0.11-0.53) 0.12 (0.04-0.34)

NS 0.0002 0.0001

4.8 2.8 1.0 0.5

0.58 (0.34-0.98) 0.20 (0.09-0.4) 0.10 (0.04-0.29)

0.038 0.0001 0.0001

4.2 2.5 1.3

0.58 (0.34-1.02) 0.29 (0.15-0.59)

0.054 0.0001

NS NS

4.8 2.0 1.5 0.2

0.40 (0.25-0.65) 0.31 (0.12-0.79) 0.04 (0.006-0.30)

0.0001 0.0001 0.0001

0.049 0.056 0.10

3.4 2.1 2.1 1.6

0.62 (0.34-1.15) 0.62 (0.33-1.14) 0.47 (0.24-0.92)

0.124 0.121 0.025

0.51 (0.27-0.98) 0.54 (0.28-1.04) 0.38 (0.2-0.8)

0.039 0.059 0.007

2.1 2.6 1.8

1.23 (0.8-1.97) 0.85 (0.12-0.85)

0.378 0.87

2.13 (1.25-3.63)

0.004 0.79

2.7 1.9

0.69 (0.43-1.12)

0.128

1.4 4.0

2.94 (1.83-4.7)

0.0001

3.9 (2.3-6.7)

0.0001

3.1 1.8

0.58 (0.36-0.92)

0.019

0.51 (0.31-0.83)

0.006

3.3 1.3

0.39 (0.23-0.65)

0.0001

0.37 (0.22-0.63)

0.0002

0.09

NS, Not significant. Overall incidence 2.3%.

*Reference group.

abnormalities was 7.8% (Table VI). There was a significant increase in odds ratio for labor abnormalities noted with the larger body mass index categories, the greatest gestational weight gain group, private patients, nulliparous patients, patients delivering male infants, patients with hypertension, and fetal macrosomia. After adjusting for these multiple factors, labor abnormalities had significantly higher odds ratios in private patients, blacks, nulliparous patients, and patients with a macrosomic fetus but reduced odds ratio in the tallest patient group. The risk of labor abnormalities did not seem to be significantly influenced by maternal age, education attainment, admitted substance abuse, pregnancy duration, nor marital status. There were significant trends in both weight gain and body mass index. A difference in weight gain of 10 pounds corresponds to an odds ratio of 2 (P < 0.0001) and a difference of 5 body mass index units corresponded to an odds ratio of about 1.65 (P < O.OOO\). Labor abnormality was cited as the most frequent indication for unscheduled

cesarean section and accounted for 40% of these operations in this study. The overall incidence of oxytocin induction was 13.7%. There was a significant twofold increase in the odds ratio for induction observed in the highest body mass index quartile and a 1.5-fold increase in the highest weight gain category. Significantly higher odds ratios were noted in postdates patients, hypertensive patients, diabetics, and married patients. Oxytocin induction was less frequent in blacks. After adjusting for these various risk factors, only the higher body mass index groups, the postdates patients, the diabetics, the hypertensives, and the LBW cases had significantly increased risks for induction. Black patients had a decreased risk. Oxytocin augmentation was used in 16.1 % of patients. The odds ratio was significantly increased in the higher weight gain group and the hypertensive patients, with trends noted in association with increasing body mass index, prepregnancy weight, decreasing rna-

362 Johnson, Longmate, and Frentzen

August 1992

Am

J Obstet Gynecol

FETAL LOW BIRTH WEIGHT=2.3%

I PRE-PREG. WT. 2

I

I

I

PRE-PREG. WT. 3

4

PRE-PREG. WT. 4 NETWT. GAIN 2 I

p<0.001

NETWT. GAIN 3

I I 0.1

I 0.2

I

0.5

1

NETWT. GAIN 4 I 2

Odds Ratio Fig. 6. This graph illustrates prepregnancy weight and net weight gain unadjusted odds ratios and 95% confidence intervals for LBW. There was stepwise reduction in risk of fetal LBW noted with rising prepregnancy weight. Net gestational weightdid not demonstrate significant decrease in odds ratio except for those patientsgaining>33 pounds. Adjusted trends testsweresignificant at p < 0.001.

ternal height, and the male fetus. The risk was significantly less in the parous patient. After adjusting, only nulliparity was associated with an increased risk of oxytocin augmentation. Teenagers were less likely to receive oxytocin augmentation. FHR abnormalities. The overall incidence of intrapartum FHR abnormalities was 27% (Table VII). The odds ratio was significantly increased for the highest body mass index category, although maternal prepregnancy weight, maternal height, and maternal gestational weight gain were not associated with increased odds ratios. After adjusting for appropriate covariables, we noted statistically significant odds ratios for body mass index, nulliparity, postdatism, macrosomia, black patients, fetal male gender, and older maternal age. The trends analysis showed no significant association with weight gain and only weak evidence of an association with body mass index (p = 0.018). FHR abnormalities were cited as the major cause for cesarean section in about 25% of the unscheduled cesarean sections in this study. Meconium staining. The overall frequency of meconium staining in the study population was 21.5% (Table VIII). There was a significant increase in the odds ratio noted with the larger body mass index categories, the larger prepregnancy weight quartiles, black patients, unmarried patients, and nulliparous patients. After adjusting for these risk factors, increased risks for meconium staining were found with high prepregnancy weight, short maternal stature, high gestational

weight gain, blacks, nulliparous patients, and admitted substance abusers. The trends test indicated an increased risk with weight gain (odds ratio 1.1 for 10 lbs, p = 0.0003) and with body mass index (odds ratio 1.22 for 5 units, p = 0.0001). Curiously, postdatism and LBW were not associated with significantly increased odds ratios for meconium staining in this study. Apgar scores and umbilical artery pH. The overall frequency of l-minute Apgar score $7 was 18.3%. Increased odds ratios were noted for increased gestational weight gain, nulliparous patients, and patients with hypertension. These same relationships pertained after adjusting. Black patients were also at greater risk. We found no associations for maternal prepregnancy weight, height, and body mass index. The overall frequency of 5-minute Apgar score $7 was 2.5%. There was a significant odds ratio increase in nulliparous patients, teenagers, and patients with hypertension. After adjusting, only nulliparity was associated with an increased risk. The mean umbilical artery pH - 2 SD is 7.12 for this patient population. The overall incidence of a pH <7.12 was 1.5%. No significant associations were noted with body mass index categories, prepregnancy weight, maternal height, or gestational weight gain. A significant association was noted for teenage and nulliparous patients. Adjusting for these findings revealed a significant association only for nulliparous patients. Resuscitation. Resuscitation, including assisted res-

Increased maternal weight and pregnancy outcome 363

Vol ume 167 Nu mbe r 2

Table IV. Unsche d u led ces arean sec tion Odds ratio and 95 % confidence interva l

Characteristic

Prepregnancy weight quarti le (lb) I'" ($ 116) 2 (117-132) 3 (133-155) 4 (> 155) Height (in) 1* «62) 2 (62-65) 3 (> 65) Body mass index category, National Academy of Science Low* « 19.8) Medium (19.8-26) High (27-29) Obese (>29) Weight gain (lb) 1* « 16) 2 (16-25) 3 (26-35) 4 (>35) Private physician No* Yes First birth Yes* No Matern al age (yr) < 20 20-26* > 26 Birt h weight (kg) < 2.5 2.5-4.0* > 4.0 Diabetes No" Yes Hypert ension No* Yes Edu cation 12th Grade 12th Grade* > 12th Grade

9.5 11.2 12.8 14.2 15.5

1.2 (0.87-1.67)

Adjusted odds ratio ami 95 % confidence interva l

0.25 0.034 0.004

104 (1.02-1.92)

1.6 (1.15-2.14)

p Value

0.87 0.11 0.74

0.58 (0042-0.8)

0.77 (0.58-1.04)

0.087 0.001

004 (0.28-0.58)

0.0019 0.0001

14.2

1.49 (1.11-2.01) 2.16 (1.46-3.18) 1.82 (1.26-2.6)

0.008 0.0001 0.001

1.5 (1.1-2.2) 1.38 (1-1.9)

0.12 0.0101 0.043

8.9 7.8 10.3 16.3

0.86 (0.56-1.34) 1.178 (0.8- 1.73) 1.988 (1.39-2.83)

0.5 1 0.400 0.000 1

0.95 (0.6-1.5) 1.3 (0.86-1.95) 1.95 (1.32-2.87)

0.82 0.21 0.0006

11.4 27.5

2.96 (1.92-4.58)

0.000 1

2.6 (1.57-4.29)

0.0001

15.8 9.1

0.53 (0043-0.66)

0.0001

0.385 (0.29-0.5)

0.0001

0.68 (0.5-0.9)

0.009

1.36 (1.0-1.83)

0.04

1204

9.6

8.3 12.0

1604

0.61 (0.44-0.84)

10.5 11.6 14.3

0.895 1.27 (0.98-1.64)

0.07

14.9 9.6 27.5

1.64 (0.855-3.16)

0.13

3.57 (2.76-4.6)

0.000 1

3.77 (2.8-5.0)

0.0001

2204

2.21 (1.36-3.599)

0.00 1

1.7 (1-2.9)

0.046

11.5 19.3

1.84 (1.24-2.74)

0.002

0.16

0.834 (0.66-1.06)

0.14

0.27

1.787 (1.33-2.4 1)

0.0001

0.12

11.6

10.0 11.7 19.2

NS

0.16

NS, Not significant. Overall inciden ce 11.9%.

*Reference group.

pir ation with a ma sk a nd oxyge n o r in tubati on, was repo rt ed with a freque ncy of 24 .5 % in this obstetri c population . In m other s with a h igh bo d y mass index a nd h igh gesta tion al weight ga in , th e odds ratios we re sign ifican tly in cr eased I .5-fold . Increases we r e also not ed in delive r y of th e fir st child and in th e cas e of fe ta l ma crosomia. Neither p r epre gna ncy weigh t o r maternal he ight we re a ssociated wit h increased ris k of resus citation. Adj usting for th es e r isk fac tors fa iled to demonstrate any statistically significa n t asso ciation s between resuscitatio n and p repregnancy weight, maternal height, or weight gain durin g p regnancy.

Comment T h is is o ne of the first stud ies evaluating pregnancy outco me in regard to t he bod y ma ss index ca te go ries recommended by t he National Academ y of Scie nces .' This stu d y ad d r esses a number of the researc h re com m end ations m ade in that p u blication . It identifies cer ta in effects of overall ge statio nal weig ht gai n with in specific ethnic grou ps and among wo me n of d ifferent ages. It examines the effects of weight ga in o n mat ernal a nd perina tal o u tco mes in m arke d ly and moderately obese women , and it test s th e r anges of recommended wei ght gai n against outcomes .

364 Johnson, Longmate, and Frentzen

August 1992

Am

J Obstet Gynecol

UNSCHEDULED CESAREAN SECTION=11.9% BMIHI BMIOB WT. GAIN >35

NULlIP. PRIV. FETAL MACRO

OLDER TEEN HT.62"-65" HT.>65"

0.2

0.5

1

2

5

Odds Ratio Fig. 7. This graph illustrates odds ratios and 95% confidence intervals for cesarean section, observed for number of demographic, morphologic, and obstetric characteristics after adjustment by stepwise logistic regression. Patients with high body mass index (BMl) and high gestational weight gain were noted to have elevated odds ratios. Nulliparous patients, private patients, and older patients, were at increased risk. Patients delivering macrosomic infants appeared to be at greatest risk. Taller patients and teenagers had reduced odds ratios. Adjusted trends tests demonstrated significant risk for unscheduled cesarean section associated with increasing body mass index, maternal weight gain, and birth weight (p < 0.0001).

Although this is a longitudinal retrospective study with some of the attendant disadvantages, it would be very difficult to execute a randomized study to assess the effects of maternal weight gain. Relying on patient recall for prepregnancy weight may be considered a limitation of this study, but Susser" observed that "patient reported weight has been shown to be reliable within a standard deviation of about 1.5 kg." In comparison with previous studies, the present investigation may be more accurate in that the duration of the pregnancy, and the outcome variables were either determined by measurement or ascertained by attending obstetric staff. Patients with selected medical and surgical illnesses were excluded. Also, this study has the advantage of reflecting recent improvements in obstetric, anesthetic, and pediatric care. The question of what is the optimal weight gain in pregnancy is clearly a very complex issue. In this study we found that both increasing prepregnancy weight

and increasing gestational weight gain were associated with increased frequencies of fetal macrosomia, labor abnormalities, postdatism, meconium staining, and unscheduled cesarean section and with a decreased frequency of LBW. We have elected to focus the discussion mostly on the association of maternal weight gain to birth weight and unscheduled cesarean section rate. In assessing the clinical implications of the body mass index, it may be important to evaluate maternal weight and height individually because there may be marked variations in these characteristics for women of similar body mass index. For example, in the National Academy of Sciences medium body mass index category, maternal weight could vary from 88 to 202 pounds (229% increase) whereas height could vary from 55.9 inches to 74 inches (132% increase)." In the present study, in the adjusted analyses of unscheduled cesarean section, height exhibited a more significant effect than body mass index or prepregnancy weight. Maternal

Increased maternal weight and pregnancy outcome 365

Volume 167 Number 2

Table V. Gestational age >42 weeks Odds ratio and 95% confidence interval

Characteristic

Prepregnancy weight quartile (lb) 1* (:s:1I6) 2 (117-132) 3 (133-155) 4 (>155) Height (in) I «62) 2 (62-65) 3 (>65) Body mass index category, National Academy of Science Low* «19.8) Medium (19.8-26) High (27-29) Obese (>29) Weight gain (lb) 1* «16) 2 (16-25) 3 (26-35) 4 (>35) Weight gain, National Academy of Science Obese plus high Within range Low* Ethnic group White* Black Other Private physician No*

Yes

Married No* Yes Tobacco, alcohol, drugs No*

Yes

Maternal age (yr) <20 20-26* >26 Birth weight (kg) <2.5 2.5-4.0* >4.0

Adjusted odds ratio and 95% confidence interval

p Value

1.75 (1.32-2.33) 1.56 (1.14-2.33)

0.68 0.0001 0.0001

7.2 8.5 12.7 11.1

1.2 (0.84-1.72) 1.89 (1.34-2.65) 1.62 (1.14-2.29)

0.31 0.0001 0.007

6.9 10.3 10.4

1.56 (1.05-2.32) 1.57 (1.04-2.36)

0.028 0.0321

0.23 0.92

8.1 9.7 12.2 1I.5

1.22 (0.896-1.66) 1.58 (1.03-2.4) 1.49 (1.01-2.2)

0.207 0.0341 0.043

0.06 0.13 0.025

8.5 8.3 9.1 11.7

0.98 (0.63-1.5) 1.08 (0.73-1.61) 1.42 (0.98-2.06)

0.913 0.693 0.06

1.7 (1.27-2.35) 1.3 (0.97-1.9)

0.0001 0.075

11.9 7.0 3.6

0.553 (0.43-0.71) 0.28 (0.7-1.15)

10.1 3.7

1.03 (0.65-1.62) 1.16 (0.76-1.76) 1.33 (0.90-1.98)

0.89 0.47 0.14

0.0001 0.059

0.64 (0.48-0.85)

0.0016 0.08

0.34 (0.12-0.93)

0.028

0.28 (0.1-0.79)

0.014

8.7 11.2

1.31 (1.04-1.65)

0.023

8.7 11.9

1.42 (1.122-1.8)

0.003

0.83 (0.63-1.09)

0.171

0.69 (0.5-0.94)

0.Dl8

0.67 (0.49-0.91)

0.008

2.04 (1.52-2.75)

0.0001

1.9 (1.37-2.6)

0.0001

11.9 9.5 7.2

9.4 11.1 7.9 0.0 9.1 17.0

0.54 1.4 (1.08-1.82)

0.0085 0.77

Overall incidence 9.8%. *Reference group.

height probably serves as a better reflection of pelvic size when analyzed alone than when expressed in the ratio that defines body mass index. A marked increase in fetal macrosomia was noted with increasing maternal body mass index. The adjusted odds ratios for maternal weight gain and prepregnancy weight were both markedly elevated. The model used for adjustments assumed that these characteristics are additive, because no interactions were detected. If these associations were additive, women with a body mass index >29 who gain >30 pounds

during pregnancy would be predicted to have a fourfold to fivefold increase in the odds ratio for macrosomia in comparison with the reference population. These preliminary findings suggest that it might be advisable to limit weight gain in obese pregnant women. These results are at variance with previous studies reporting that in obese women weight gain did not influence birth weight. However, several of these studies did not adjust for medical-surgical illnesses and were characterized by smaller numbers.v " Their results might have been influenced by type II statistical error.

366 Johnson, Longmate, and Frentzen

August 1992 Am J Obstet Gynecol

Table VI. Labor abnormalities Odds ratio and 95% confidence interval

Characteristic

Prepregnancy weight quartile (lb) 1* ($116) 2 (117-132) 3 (133-155) 4 (>155) Height (in) 1* «62) 2 (62-65) 3 (>65) Body mass index category, National Academy of Science Low* «19.8) Medium (19.8-26) High (27-29) Obese (>29) Weight gain (lb) 1*«16) 2 (16-25) 3 (26-35) 4 (>35) Ethnic group White* Black Other Married No* Yes Private physician No* Yes Parity 1* >1 Fetal sex male No* Yes Maternal age (yr) <20 20-26* >26 Hypertension No* Yes Birth weight (kg) <2.5 2.5-4.0* >4.0

Adjusted odds ratio and 95% confidence interval

p Value

6.4 7.9 7.9 9.0

1.26 (0.86-1.85) 1.26 (0.86-1.85) 1.46 (1.003-2.13)

0.23 0.24 0.05

9.0 8.6 6.0

0.96 (0.66-1.38) 0.65 (0.43-0.98)

0.81 0.04

6.2 7.7 10.8 8.7

1.26 (0.89-1.79) 1.78 (1.11-2.81) 1.45 (0.94-2.25)

0.19 O.oI5 0.09

6.0 5.5 7.2 10.0

0.918 (0.55-1.54) 1.223 (0.77-1.93) 1.746 (1.14-2.67)

0.746 0.388 0.010

0.96 (0.56-1.65) 1.22 (0.76-1.97) 1.53 (0.97-2.41)

0.89 0.40 0.059

7.2 8.6 7.4

1.22 (0.93-1.59) 1.03 (0.37-2.9)

0.14 0.95

1.68 (1.26-2.25)

0.0003 0.82

8.6 6.7

0.77 (0.59-1.003)

0.05

7.4 17.0

2.54 (1.5-4.3)

0.0001

2.63 (1.48-4.68)

0.0008

11.3 5.2

0.44 (0.33-0.57)

0.0001

0.34 (0.25-0.46)

0.0001

6.5 9.0

1.42 (1.09-1.85)

0.009

1.36 (1.03-1.80)

0.02

0.65 (0.47-0.91)

0.01

0.88 0.72 0.12

0.57 (0.42-0.78)

0.20 0.0004

0.42 0.10 0.34

0.08

7.7 8.5 6.3

0.99 (0.67-1.22)

0.50

0.73 (0.51-1.04)

0.08

0.81

7.5 12.9

1.84 (1.15-2.94)

0.009

0.16

0.188 (0.026-1.36)

0.06

0.06

2.679 (1.96-3.67)

0.0001

1.4 6.8 16.3

3.18 (2.25-4.495)

0.0001

Overall incidence 7.8%. "Reference group.

The increased risks associated with high prepregnancy weight and high weight gain during pregnancy observed in this study have been amply demonstrated in many previous studies. s, 9,10, IS Yet the recent National Academy of Science recommendations advocate increasing maternal weight gain during pregnancy. These recommendations appear to be based primarily on earlier observations that (1) LBW is associated with increased perinatal mortality and infant morbidity and (2) increased maternal weight gain is associated with

lower rates of LBW. The inference has been drawn that increasing maternal weight gain will reduce the frequency ofLBW and thereby reduce perinatal mortality and morbidity." These assumptions may be dangerous and costly oversimplifications. The causes of LBW are myriad and some are more hazardous than others.": 16 Prematurity accounts for a significant portion of LB W babies. A major portion of LBW term infants have no underlying fetal or maternal abnormalities. These infants are born small for familial

Increased maternal weight and pregnancy outcome 367

Volume 167 Number 2

Table VII. FHR abnormalities

Prepregnancy weight quartile (lb) 1* ($116) 2 (117-132) 3 (133-155) 4 (> 155) Height (in) 1* «62) 2 (62-65) 3 (>65) Body mass index category, National Academy of Science Low* «19.8) Medium (19.8-26) High (27-29) Obese (>29) Weight gain (lb) 1* «16) 2 (16-25) 3 (26-35) 4 (>35) Ethnic group White* Black Other Gestational age :2:42 wk No* Yes Private physician No* Yes Parity 1* >1 Fetal sex male No* Yes Maternal age (yr) <20 20-26* >26 Hypertension No* Yes Birth weight (kg) <2.5 2.5-4.0* >4.0

Adjusted odds ratio and 95% confidence interval

Odds ratio and 95% confidence interval

Characteristic

p Value

25.8 26.3 26.4 29.5

1.025 (0.82-1.28) 1.033 (0.83-1.29) 1.207 (0.97-1.51)

0.83 0.78 0.10

0.92 0.98 0.52

31.4 26.9 25.2

0.806 (0.64-1.01) 0.736 (0.58-0.94)

0.06 0.01

0.88 0.08

23.0 27.2 29.1 31.0

1.25 (1.023-1.54) 1.38 (1.029-1.85) 1.506 (1.164-1.95)

0.03 0.03 0.002

0.11 0.17 0.01

21.6 19.4 18.3 25.0

0.96 (0.73-1.26) 1.09 (0.86-1.38) 1.09 (0.86-1.38)

0.771 0.489 0.489

24.9 30.2 22.2

1.30 (1.108-1.:-3) 0.86 (0.45-1.65)

0.001 0.65

1.36 (1.15-1.61)

0.0003 0.89

25.9 37.1

1.69 (1.32-2.16)

0.0001

1.84 (1.42-2.38)

0.0001

26.7 34.0

1.41 (0.94-2.13)

0.10

32.6 22.9

0.616 (0.53-0.72)

0.0001

0.55 (0.46-0.66)

0.0001

24.0 29.9

1.355 (1.16-1.59)

0.0001

1.38 (1.17-1.63)

0.0001

1.33 (1.06-1.67)

0.83 0.67 0.29

0.08

0.93

29.3 24.8 28.4

1.25 (1.04-1.50)

0.02

1.198 (0.98-1.46)

0.08

26.5 35.9

1.55 (1.13-2.15)

0.007

0.12

1.179 (0.715-1.94)

0.52

0.28

0.69 (0.531-0.901)

0.006

31.1 27.7 20.9

1.385 (1.129-1.699)

0.65 (0.49-0.87)

0.0014

0.003

Overall incidence 27%. *Reference group. or constitutional reasons. In the absence of asphyxial insults, which are mostly preventable, these babies have excellent outcomes." 17 An increase in maternal weight gain may reduce the frequency of this type Of LBW infant, but there is little if any evidence of an associated improvement in perinatal mortality or morbidity. Intrinsic abnormalities in the fetus (congenital anomalies, infections, chromosomal abnormalities, etc.) account for a small percentage of LBW infants but contribute significantly to poor outcomes, including death

and morbidity. Maternal illnesses account for another portion of LBW infants, and asphyxial complications are primarily responsible for the poorer outcome noted in these cases. Unfortunately, in prior studies of the mortality and morbidity associated with LBW, the consequences of prematurity, intrinsic fetal abnormalities, and asphyxial events were not taken into consideration. There is little experimental or clinical evidence that increased maternal weight gain in pregnancy will reduce the wastage associated with these forms of LBW.

368 Johnson, Longmate, and Frentzen Am

August 1992

J Obstet Gynecol

Table VIII. Meconium-stained amniotic fluid Odds ratio and 95% confidence interval

Characteristic

Prepregnancy weight quartile (lb) 1* (s116) 2 (117-132) 3 (133-155) 4 (> 155) Height (in) 1* «62) 2 (62-65) 3 (>65) Body mass index category, National Academy of Science Low* «19.8) Medium (19.8-26) High (27-29) Obese (>29) Weight gain (lb) 1*«16) 2 ( 16-25) 3 (26-35) 4 (>35) Ethnic group White* Black Other Married No* Yes Tobacco, alcohol, drugs No* Yes Parity 1* >1 Maternal age (yr) <20 20-26* >26 Education <12th Grade 12th Grade* >12th Grade Birth weight (kg) <2.5 2.5-4.0* >4.0

Adjusted odds ratio and 95% confidence interval

p Value

17.7 21.0 22.5 25.2

1.237 (0.97-1.59) 1.34S (1.05-1.73) 1.571 (1.23-2.00)

0.09 0.02 0.0001

1.29 (0.99-1.68) 1.44 (1.11-1.87) 1.71 (1.3-2.2)

0.49 0.005 0.0001

21.7 23.1 19.1

1.08 (0.84-1.39) 0.849 (0.65-1.11)

0.54 0.24

0.70 (0.58-0.85)

0.61 0.0003

16.5 21.6 26.7 25.8

1.39 (1.11-1.75) 1.84 (1.35-2.52) 1.756 (1.33-2.33)

0.004 0.0001 0.0001

21.6 19.4 IS.3 25.0

0.874 0.816 1.214

0.38 0.15 0.14

0.99 (0.73-1.36) 0.99 (0.74-1.34) 1.44 (1.09-1.89)

0.98 0.98 0.009

18.8 25.7 IS.5

1.5 (1.3-1.49) 0.98

0.0001 0.95

1.70 (1.41-2.06)

0.0001 0.65

23.8 18.8

0.737 (0.62-0.88)

0.001

21.1 22.4

1.081

0.39

1.29 (1.07-1.58)

0.008

23.8 19.9

0.797 (0.67-0.95)

0.009

0.7 (0.58-0.S5)

0.0002

22.7 19.8 23.7

1.19 (0.98-1.46)

0.08

1.26 (1.02-1.56)

0.03

1.33 (1.06-1.66)

0.012

22.9 20.5 20.4

1.148

0.14

1.21 (1.00-1.45)

0.04

0.99

0.94

0.76

0.72 (0.39-1.34)

0.30

0.28

1.258 (0.98-1.62)

0.07

16.2 21.2 25.3

0.94 0.37 0.89

0.14

0.92

1.31 (0.99-1.7)

0.046

Overall incidence 21.5%. *Reference group.

In fact, Kleinman'S in a study of 3946 cases of white non-Hispanic women found that total maternal weight gain tended to overstate the association between maternal weight gain and fetal growth. He recommended the use of net weight gain rate (total maternal weight gain minus baby's birth weight divided by weeks of gestation) to assess these interrelationships. With this measure of maternal weight gain he found that an increased net weight gain was linked to a significant decrease in the frequency of term LBW infants only in women of moderate body mass index (19.8 to 26.0). In obese patients (body mass index >26.0), an increased

net weight gain tended to increase the frequency of term LBW infants. Increases in net weight gain appeared to have little impact on the frequency of preterm LBW, regardless of the mother's body mass index. In the present study we attempted to estimate the public health implications of our findings by predicting the national costs, in terms of rates of unscheduled cesarean section and low birth weight relative to differences in maternal weight gain. The recent National Academy of Science recommendations for weight gain in pregnancy' specify 28 to 40 pounds for a body mass index < I 9.8, 25 to 35 pounds for a body mass index

Volume 167 Number 2

of 19.8 to 26, 15 to 25 pounds for a body mass index of 27 to 29, and at least 15 pounds for a body mass index >26 to 29. With these ranges (and 15 to 25 pound range for a body mass index >29) we calculated the cesarean section rates for patients according to whether their weight gain was below, within range, or above the National Academy of Science recommendations. The unscheduled cesarean section rates were 7.7%, 9.6%, and 16.6%, respectively, for these three groups. With multiple logistic regression we found that if weight gain was limited in all cases to the maximum National Academy of Science recommendation, the predicted unscheduled section rate was 9.7% (Table IX). If all weight gain was limited to the lowest NAS recommendation, the predicted unscheduled section rate was 8.1 %. Assuming our statistical model is correct and that our patient population reflects the national situation, a decrease in cesarean section rate from 11.9% to 8.1 % nationally could result in annual savings of$253 to $436 million dollars." A theoretic reduction in body mass index values to a maximum of 29 or even 26 would be expected to reduce the unscheduled cesarean section rate by only 0.4% to 0.9% (Table IX). The greater effect of limiting gestational weight gain is due to the higher prevalence of excessive gestational weight gain compared with high body mass index in this population. These theoretic reductions in maternal weight would be predicted to also increase the frequencies of LBW. The LBW rates associated with maternal weight gain below, within range, or above National Academy of Science recommendations were 4.7%, 1.8%, and 1.1%, respectively. Again with multiple logistic regression, we found that limiting all weight gain to the maximum National Academy of Science recommendations yielded a predicted LBW rate of 2.5% (Table X). If all weight gain was limited to the lowest National Academy of Science recommendation, the predicted LBW frequency was 3.0%. Again, the predicted influence of reduced body mass index is a lesser increase in LBW frequency. Limiting body mass index to a maximum of 29 or 26 results in a predicted increase in LBW rate of only 0.1 % to 0.2% (Table X). Assuming our statistical model is correct and that this study population reflects the national experience with LBW, we estimate that an increase in the national frequency of this type of low birth weight from 2.3% to 3.3% would result in additional hospital expenses of about $1 to $2 million dollars per annum. Recent studies have shown no increase in long-term morbidity.": 20. 21 The net effect appears to argue strongly for limiting weight gain in pregnancy. In summary, the results of this study indicate that

Increased maternal weight and pregnancy outcome 369

Table IX. Predicted unscheduled cesarean section rates with decreased weight gain and body mass index Body mass index Weight gain

Observed (%)

Observed Compliant Low

11.9 9.7 8.1

Maximum of 26 (%)

11.4 9.3 7.7

11.0 9.0 7.5

Table X. Predicted LBW rates according to gestational weight gain and body mass index Body mass index Weight gain

Observed (%)

Observed Compliant Low

2.3 2.5 3.0

Maximum of 26 (%)

2.4 2.6 3.1

2.5 2.7 3.3

either high prepregnancy weight or high weight gain during pregnancy lead to increased cesarean sections and other complications. These complications seem to outweigh any purported medical benefits. Furthermore, the additional expenses required to deal with these consequences on a national basis could be substantial. Recent recommendations advising additional weight gain in pregnancy need further evaluation before implementation. REFERENCES 1. Report of a special panel on desired prenatal weight gains for underweight and normal weight women. Public Health Rep 1990; 105:24-8. 2. Worthington-Roberts B. Directions for research on women and nutrition. Am J Health Promotion 1990;5: 63-9. 3. Ruge S, Andersen T. Obstetric risks in obesity: an analysis of the literature. Ob/Gyn Surv 1985;40:57-60. 4. Seidman DS, Ever-Hadani P, Gale R. The effect of maternal weight gain in pregnancy on birth weight. Obstet Gynecol 1989;74:240-6. 5. National Academy of Science. Nutrition during pregnancy. Washington, DC: National Academy Press, 1990. 6. Committee on Maternal Nutrition. Maternal nutrition and the course of pregnancy. Washington, DC: National Academy of Sciences, 1970. 7. Task Force on Nutrition. Assessment of maternal nutrition. Chicago: American College of Obstetricians and Gynecologists, American Dietetic Association, 1978. 8. Abrams BF, Laros RK. Prepregnancy weight, weight gain, and birth weight. AM J OBSTET GYNECOL 1986;154: 503-9. 9. Shepard MJ, Hellenbrand KG, Bracken MB. Proportional weight gain and complications of pregnancy, labor, and

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Am

10. 11.

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delivery in healthy women of normal prepregnant stature. AM] OBSTETGYNECOL 1986;155:947-54. Larsen CE, Serdula MK, Sullivan KM. Macrosomia: influence of maternal overweight among a low-income population. AM] OBSTETGYNECOL 1990;162:490-4. Frentzen BH, Dimperio DL, Cruz AC. Maternal weight gain: effect on infant birth weight among overweight and average-weight low-income women. AM] OBSTET GYNECOL 1988; 159: 1114-7. Scott A, Moar V, Ounsted M. The relative contribution of different maternal factors in large-for-gestational-age pregnancies. Eur ] Obstet Gynecol Reprod BioI 1982;13:269-77. Johnson SR, Kolbert BH, Varner MW, Railsback LD. Maternal obesity and pregnancy. Surg Gynecol Obstet 1987;164:431. Susser M. Review of dietary behavior during pregnancy. In: Dobbing], ed. Maternal nutrition in pregnancy: eating for two? London, Academic Press, 1981:64-5. Gabbe SG. Intrauterine growth retardation. In: Gabbe SG, Niebyl]R, Simpson]L, eds. Obstetrics-normal and problem pregnancies, ed 2. New York: Churchill Livingstone 1991:924. Creasy RK, Resnik R. Intrauterine growth retardation. In: Creasy RK, Resnik RK, eds. Maternal fetal medicine: principles and practice, ed 2. Philadelphia: WB Saunders, 1989:547. Fanaroff AA, Martin R], Miller MA. Identification and management of high-risk problems in the neonate. In: Creasy RK, Resnik RK, eds. Maternal fetal medicine: principles and practice, ed 2. Philadelphia: WB Saunders, 1989:1167. Kleinman ]C. Maternal weight gain during pregnancy: determinants and consequences. Washington, DC: U.S. Department of Health and Human Services, National Center for Health Statistics, 1990; Working Paper Series, no. 33. Schwarz RH. Presidential address to the American College of Obstetricians and Gynecologists. ACOG Newsletter 1991; August:2. Westwood M, Kramer MS, Munz D, Lovett ]M, Watters GV. Growth and development of full-term nonasphyxiated small-for-gestational newborns: follow-up through adolescence. Pediatrics 1983;71:376-82. Berg AT. Indices of fetal growth-retardation, perinatal hypoxia-related factors and childhood neurological morbidity. Early Hum Devel 1989;19:271-83.

Editors' note: This manuscript was revised after these discussions were presented.

Discussion Newport News, Virginia. Johnson et al. examine carefully the emphasis placed in recent years on the notion that "more is better" when referring to weight gain in pregnancy. It has been widely held that this emphasis on maximizing pregnancy weight gain reached its pinnacle in 1989 with the publication of results from the National Natality Study by the National Center for Health Statistics. "It was noted in that publication that LBW was 2.3 times more likely, and fetal death 1.5 times more likely, in women who gained <20 pounds during pregnancy when compared with those who gained >20 pounds. In addition, it was noted that 20% of all black mothers in 1980 gained < 16 pounds during pregnancy and had the poorest pregnancy outcomes. These results might lead one to believe that there is a direct correlation between the amount DR. BARRY GROSS,

J Obstet Gynecol

of weight gained in pregnancy and the health of the baby delivered and that increasing the amount of weight gained in pregnancy will reduce the incidence of LBW infants. Johnson et al. have demonstrated that while this may indeed be true in women who start pregnancy at lower body weights, it does not translate with the same validity to those women who begin pregnancy overweight. The first published study of diet and pregnancy was by Prochownick" in 1901. This work demonstrated that restricted food intake throughout pregnancy reduced the birth weights of males by approximately 400 gm and those of females by 500 gm. Indeed, over the past century there have been many varying changes in recommendations regarding weight gain in pregnancy. Over most of this time the recurrent theme was restriction of caloric intake, because it was felt that this restriction could prevent large babies and associated difficult labors and deliveries." 4 This approach is entirely understandable because maternal mortality was very high and delivery by cesarean section was often an act of desperation. Later in the century controlling weight gain during pregnancy was advocated to prevent toxemia.' Studies published in the 1950s, 1960s, and early 1970s generally indicated that an average weight gain of 12.5 kg (27.5 lb) was considered normal. In 1970 the Food and Nutrition Board's Committee on Maternal Nutrition and, a few years later, the American College of Obstetricians and Gynecologists published the average desirable weight gain as 24 pounds.v ' In fact, the recommended gestational weight gains have essentially doubled between 1930 and 1990, from 15 pounds in 1930 to 30 pounds in the late 1980s. Before publication of the National Natality Study," generally recommended weight gain was on the order of 10 to 12 kg (22 to 27 pounds) during pregnancy. Mirroring the findings of that study, most publications in obstetrics at that time, including Standards of the American College of Obstetricians and Gynecologists, generally noted that regardless of how much women weigh before they become pregnant, the gaining of between 26 and 30 pounds during pregnancy could improve the outcome of pregnancy and reduce their chances for having the pregnancy end with fetal morbidity." There is little doubt that the plight of the LBW infant has deserved the highest order of attention by our specialty. A large body of evidence indicates that the amount of gestational weight gain is a determinant of fetal growth." Lower total weight gains are associated with an increased risk of LBW babies with higher perinatal mortality. In this paper, Johnson et aI., have refocused our attention to the opposite end of the continuum, excessive maternal weight gain and its outcome. Both increasing maternal prepregnancy weight and increasing maternal gestational weight gain were found to be associated with increased frequencies of fetal macrosomia, labor abnormalities, FHR abnormalities, postdatism, meconium staining, and unscheduled cesarean section.

Increased maternal weight and pregnancy outcome 371

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Indeed, most studies have demonstrated an increased risk of hypertension, preeclampsia, and gestational diabetes in patients manifesting excessive maternal weight gain. Babies are bigger, and cesarean section rates are higher. Higher birth weights are associated with prolonged labor, shoulder dystocia, birth trauma, and asphyxia. Many believe that postpartum hemorrhage, puerperal infection, and venous thrombosis are more common. Surgical morbidity and mortality rises, because patients are more difficult to administer anesthesia to, have more postanesthesia complications, and have more wound complications. Although the encouraging of weight gain has been seen as a means by which we might lower the number of LBW babies, it is clear that the weight that is gained is not always either nutritionally adequate or appropriate. Weight gain is often not a reflection of a nutritionally balanced diet." Johnson et al. used both actual maternal weight gain and body mass index as tools in this evaluation. Of interest is body mass index, which is defined as prepregnancy weight in kilograms divided by height in meters squared (or "weight for height") and has been endorsed by the National Academy of Science, in their 1990 publication Nutrition During Pregnancy, as a tool for patient evaluation. Johnson et al.s data appear to demonstrate what others have noted, e.g., that in the initial risk assessment of outcomes related to maternal weight, the calculation of maternal body mass index offers no advantage over simply weighing the patient. I I It is well known that the effect of gestational weight gain on fetal growth is modified by the mother's prepregnancy weight for height. Multiple studies have demonstrated that the effect of a given weight gain (or rate of weight gain) on fetal growth is greatest in thin women and least in overweight women.": 13 Prepregnancy weight for height, or body mass index, can be a determinant of fetal growth independent of the effect of gestational weight gain. Studies show that women who are thinner before pregnancy tend to have babies that are smaller than those of their heavier counterparts with the same gestational weight gain. A desirable pregnancy weight gain seems to be, in general, inversely proportional to the body mass index of the patient. 12 Studies also suggest that increases in maternal fat, lean tissue, and body water may each be associated with increased fetal growth. Problems associated with this increased fetal growth, as demonstrated by Johnson et al., appear to be more pronounced in short women (high body mass index). The data presented by the authors clearly suggests that there are many good reasons to suggest limitations on weight gain in selected pregnancies. Although this principle is at variance with many of the nutritional guidelines published in the mid 1980s, it does agree with the most recent (1990) suggestions by the National Academy of Science. The Academy has divided all pregnancies into four groups by determining prepregnancy weights-for-heights. As one might expect, as the individual groups' body mass index increased, its suggested weight gain decreased. Individualization of

weight gain and appropriate dietary instruction therefore would seem to be the prescribed manner to approach the topic of appropriate pregnancy weight gain. Although the degree of weight gain restriction in the overweight pregnant woman may be debated (as it has over the past 91 years), it is clear from this study by Johnson et al. that only by aggressively managing the weight gain of patients from both ends of the prepregnancy weight spectrum and pregnancy weight gain spectrum will we be able to reduce significantly maternal and neonatal morbidity and mortality and the associated physical and financial resources that those morbidities exhaust. REFERENCES I. National Center for Health Statistics. Advance report of

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final natality statistics, 1987. Mon Vital Stat Rep 1989;38: 1-48. Prochownick L. Ueber Ernahrungscuren in der Schwangerschaft. Ther Monatsh 1901;15:446-63. Davis CH. Weight in pregnancy: its value as a routine test. AM] OBSTET GYNECOL 1923;6:575-81. Humphreys RC. An analysis of the maternal and foetal weight factors in normal pregnancy. J Obstet Gynaecol Br Commonw 1954;61:764-71. McIlroy AL, Rodway HE. Weight-changes during and after pregnancy with special reference to early diagnosis of toxaemia. J Obstet Gynaecol Br Empire 1937;44:221-44. National Research Council. Maternal nutrition and the course of pregnancy. Report of the Committee on Maternal Nutrition, Food and Nutrition Board, Washington, DC: 1970. Committee on Nutrition. Nutrition in maternal health care. Washington, DC: American College of Obstetricians and Gynecologists, 1974_ Nutrition during pregnancy. Washington, DC: National Academy Press, 1990. American College of Obstetricians and Gynecologists. Standards for obstetric-gynecologic services, ed 6. Washington, DC: American College of Obstetricians and Gynecologists, 1985. Abrams B, Parker J. Maternal weight gain in women with good pregnancy outcome. Obstet Gynecol 1990;76:1-7. Aaronson LS, Macnee C. The relationship between weight gain and nutrition in pregnancy. Nurs Res 1989;38: 223-7. Wolfe HM, Zadpr IE, Gross TL, Marrier SS, Sokol RJThe clinical utility of maternal body mass index in pregnancy. AM] OBSTETGYNECOL 1991;164:1307-10. Naeye RI. Maternal body weight and pregnancy outcome. Am J Clin Nutr 1990;32:273-9.

DR. HERBERT G. HOPWOOD,JR., Arlington, Virginia. I would like to ask Dr. Johnson if he had an increase in shoulder dystocia in his patients compared with his controls? DR. GENE BURKETT, Miami, Florida. The bottom line is what is the ideal pregnancy weight gain? Have you looked at the prepregnancy weight differences with the postpartum weight and related that to outcome as a means of trying to devise in your four groups what the ideal prepregnancy weight gain for each group might be? DR. JOHN F. HUDDLESTON, Atlanta, Georgia. Many of the studies associated with weight gain in pregnancy seem to take the extremes in weight gain rather than

372 Johnson, Longmate, and Frentzen

looking at the time course of weight gain. I think from a clinical point of view many of us are more concerned with the abrupt weight gain than the steady weight gain. I wonder if the time course was considered in this study. DR.JOHNJ. BRITTON, Sumpter, South Carolina. Obviously, with increasing postdatism we get more fetal macrosomia and meconium staining of the amniotic fluid, but the data seem to indicate that excessive maternal weight gain during pregnancy or the obese patient who was obese before pregnancy tends to increase postdatism. Why does this group appear to have an increase in postdatism? DR. JOHNSON (Closing). The question of what is the optimal weight gain in pregnancy is an emotional and controversial issue; and it has been for a very long time, probably because of its complexity. We found the incidence of shoulder dystocia to be significantly increased if there was macrosomia. That seemed to be the major determinant as to whether shoulder dystocia was diagnosed. We do not have analyses that would lead us to conclude what is the optimal prepregnancy weight. I think that the National Academy of Science has chosen ideal body weight, the basis of the Metropolitan Life Insurance data of 1959, to be a body mass index of 19 to 26, that is, 90% to 110% of ideal body weight.

August 1992 Am J Obstet Gynecol

Dr. Huddleston raised an interesting point about the time course of weight gain during pregnancy. We did not look at that in our population. That would be a difficult and time-consuming task because we cannot retrieve that information from our computerized data bank. Dr. Kleinman looked at the rate of weight gain during pregnancy and did not report any birth weight differences from those that we have reported here.' Why an increase in postdatism occurs is a very good question. We have tried to analyze this from our data. It does occur if the mother enters pregnancy above ideal weight or if she gains excessive weight during the course of the pregnancy. The increase in postdatism persists even after adjusting for macrosomia. We do not have a ready explanation other than it appears that excessive weight leads to prolonged pregnancy, rather than the converse. REFERENCE 1. KleinmanJC. Maternal weight gain during pregnancy: determinants and consequences. Washington, DC: U.S. Department of Health and Human Services, National Center for Health Statistics, 1990; Working Paper Series, no. 33, 1990.