- Email: [email protected]
Exercise During Pregnancy and Type of Delivery in Nulliparae
JoGNN
C L ~ I - I C ASTUDIES L,
Exercise During Pregnancy and Type of Delive y in Nulliparae T i m o t h y J. B u n g u m , DrPH, CHES, Dian L. Peaslee, RN, BAN, MS, Allen I% Jackson, EdD, Miguel A. Perez, PhD, CHES
=
Objective: To assess the association between participation in aerobic exercise during the first two trimesters of pregnancy and type of delivery in nulliparous women. Design: Nonexperimental, retrospective. Setting: A large metropolitan area in the southwestern United States. Participants: 137 nulliparous women. Outcome Measures: Method of delivery. Results: An unadjusted odds ratio showed that sedentary women ( n = 93) were 2.05 times more likely to deliver via cesarean section than active women ( n = 44), but this relationship was not statistically significant. Through logistic regression analysis with control for the mother's prepregnancy exercise program, age, use of epidural anesthesia, change in prepregnancy to delivery body mass index, labor length, whether labor was induced, and the hospital of birth, the odds of cesarean delivery were found to be 4.5 times greater for sedentary women than for active women. Conclusion: Regular participation in physical activity during the first two trimesters of pregnancy may be associated with reduced risk for cesarean delivery in nulliparous women. JOG" 29,
250-264; 2000. Keywords: ExerciseNul Iiparuepregnancy Accepted: September 1 999
The potential benefits of physical activity are well known (U.S. Department of Health and Human Services, 1996). Pregnant women often are advised to exercise but should not do so to the point of exhaustion. Exercise in certain positions and any activity that involves the potential for
258 JOG"
abdominal trauma should be avoided. The focus of this article is the relationship between physical activity during the first two trimesters of pregnancy and type of delivery.
Literature Review In recent decades pregnant women have become more likely to engage in exercise (Baddeley & Green, 1992; Wallace, Boyer, Dan, & Holm, 1986). Accordingly, health professionals have investigated the risks and benefits of exercise during pregnancy. Revelli, Durando, and Massobrio (1992) suggest that exercise benefits most healthy pregnant women who were physically active prior to conception. Three studies have shown that women can engage in aerobic exercise during healthy pregnancies without compromising fetal growth and development or complicating the processes of pregnancy, labor, or delivery (Hall & Kaufmann, 1987; Jackson, Gott, Lye, KnoxRitchie, & Clapp, 1995; Rice & Fort, 1991). Potential benefits of exercise during pregnancy include a decrease in pregnancy-related discomforts (Horns, Ratcliffe, Leggett, & Swanson, 1996; Sternfield, Quesenberry, Eskenazi, & Newman, 1995; Wallace et al., 1986), shortened labor (Kulpa, White, & Visscher, 1987; Wong & McKenzie, 1987), and perhaps an increase in the likelihood of vaginal delivery. Two studies have demonstrated a higher incidence of vaginal delivery among women who exercise (Clapp, 1990; Hall & Kaufmann, 1987). Clapp (1990), using a prospective study design, showed that women who exercised throughout their pregnancies had higher rates of vaginal births (88%) than women Volume 29, Number 3
who discontinued their exercise regimen by the end of their 1st trimester (70%). Hall and Kaufmann (1987) assessed data from 845 women who were given the option of participating in a prenatal program that involved stretching exercise and aerobic workouts on stationary bicycles. Those who participated in the most exercise sessions during pregnancy delivered vaginally in 93% of cases, while those who exercised the least delivered vaginally 71% of the time. The reasons exercise would influence type of delivery are not clear. It is hypothesized that increased or maintained fitness during pregnancy allows the mother to better manage the rigors of childbirth. Vaginal deliveries are generally preferred to cesarean sections because the risks to the mother for a cesarean delivery include infection, excessive blood loss, decreased bowel function, respiratory complications, reactions to anesthesia, longer hospital stays, and longer recovery periods (Johnson, 1994). Another benefit of vaginal rather than cesarean delivery is the lower medical cost. In 1994, delivery via cesarean section cost $3,160 more than a vaginal delivery (Centers for Disease Control and Prevention, 1994). Therefore, vaginal deliveries, when possible, are preferable to cesarean deliveries. Virtually all researchers who have assessed the effects of physical activity on delivery type have included women who have completed one or more pregnancies. In addition to parity, age (Gilbert, Nesbitt, & Danielson, 1999) and the use of epidural anesthesia during labor (Morton, Williams, Keeler, Gambone, & Kahn, 1994) have been shown to influence delivery type. It also has been suggested that hospital of birth may influence type of delivery. Because previous pregnancy has been shown to influence type of delivery (Gilbert et al., 1999), the current study included only women who had not completed a pregnancy past 23 weeks of gestation (i.e., nulliparae). The purpose of this investigation was to assess differences in rates of cesarean versus vaginal delivery among women who were physically active during the first two trimesters of their pregnancy and those who were not. A secondary objective was to investigate the association of maternal physical activity during pregnancy and newborn birth weight.
Method Participants Participants were nulliparous women who attended hospital-based childbirth education classes or a private fitness center that offered a prenatal aerobic exercise program. The childbirth education classes were offered at three private, for-profit, hospitals. These childbirth education classes met weekly for 6 weeks. Class sessions typically occurred 2-4 weeks before the
Mayl’une 2000
anticipated delivery. One of the authors (D.P.) attended the final childbirth education class session of three classes to request participants for the study. Women who were willing to participate signed an informed consent statement that explained the study’s procedures and potential risks associated with involvement. Approval to conduct the research was obtained from the participating university’s institutional review board and a similar board at each hospital. The owner of the private fitness center agreed to allow participants in the prenatal exercise class the option to participate in this project. Participants were residents of a large metropolitan area in the southwestern United States. In addition to the requirement of nulliparity, criteria for study inclusion mandated that the women be nonsmokers, expecting a singleton birth, and age 17-40 years at the time of delivery. Further, participants must have been free of gestational diabetes, preeclampsia, high blood pressure, and abnormal bleeding during the pregnancy. Participants also were asked about other pregnancy-related problems. Data were collected over an 8-week period during the spring of 1997. A checklist was used to measure physical activity. Participants self-reported the average number of times they had engaged in selected physical activities at least three times per week, for at least 20 minutes during each trimester of pregnancy. The physical activity checklist included the following activities: swimming, brisk walking, running/jogging, aerobic dance, stationary or regular bicycling, stairclimber work, racquet sports, in-line skating, and other. Women who reported regular physical activity (three or more sessions of 20 minutes or more per week) during the 1st and 2nd trimesters were labeled active. All other women were classified as sedentary. These guidelines were selected because they are similar to those recommended by the American College of Obstetricians and Gynecologists (ACOG) (1994).
Procedure Initial data were collected before the delivery, and a follow-up phone call was made approximately 2 weeks after the expected delivery date. The first data collection involved participant completion of a 3 1-item written survey. This survey produced, in addition to the previously mentioned vaiiables, information regarding the mother’s age, ethnic background, marital status, a brief medical history, and anticipated due date. A pilot test of the survey instrument was administered to seven women who had recently delivered healthy newborns. The goal of the pilot study was to identify items that were unclear or difficult to comprehend. Data from these women were not included in subsequent analyses. Only minor changes were made to the questionnaire as a result of these women’s feedback.
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TABLE 1
Characteristics of 137 Nulliparae in the Active and Sedentary Groups Variables
Age (years) Education (years) Prepregnant weight (Ib) Prepregnant body mass indexes Body mass index change Height (cm)
Active (M f SD)
Sedentay (M SD)
29.6 t 3.3 15.9 * 1.5 130.4 21.5 21.5 * 3.1 5.61 t 1.5 165.9 * 6.2
28.4 t 4.6 15.1 t 1.7 138.9 t 26.3 23.1 t 3.85 5.94 t 2.1 165.4 t 6.4
During the follow-up telephone call, mothers were asked the date of birth, birth weight, gender, the number of weeks of gestation, the mother's weight at the last check-up before giving birth, whether the labor had been induced, whether an episiotomy had been performed, whether forceps or a vacuum extractor had been used, whether an epidural had been administered, and the method of birth (vaginal or cesarean). A reminder card that listed the information that would be requested during this follow-up phone call was provided at the time the participants were recruited. Accordingly, most participants were expecting the follow-up phone call and readily reported the requested data. No review of records or follow-up calls were made to assess the reliability or validity of this data. All deliveries occurred in hospital settings under the care of a physician.
Data Analysis Descriptive statistics were calculated for all variables. The t test was used to identify differences between the active and sedentary groups. Maternal characteristics of age, education, and body mass index (BMI) were analyzed for differences between the two groups. An unadjusted odds ratio that assessed the likelihood of having a cesarean section or vaginal delivery was calculated for the two groups. A multiple logistic regression analysis was used with control for the following factors: mother's physical activity level before pregnancy, mother's age, change in prepregnancy to predelivery BMI, use of epidural anesthesia, labor length, whether labor was induced, and the hospital of birth. In this way, the odds of delivery via cesarean for active versus sedentary women were determined. These particular factors were accounted for because they have been shown to influence type of delivery. Prepregnancy exercise was controlled for to isolate the effects of exercise during pregnancy. Controlling for these variables produced an odds ratio free of the influence of major extra-
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*
t
Value 1.75 2.79 2.00 5.61 0.96 .39
p
.08 .006 .05 .02 ns ns
neous variation related to type of delivery. A goodness of fit test (Hosmer, Taber, & Lemeshow, 1991) indicated that the model fit the data adequately, p = ns.
Results A total of 164 women volunteered for the study, and data were analyzed for 137. Reasons for exclusions included the presence of diabetes ( n = l o ) , cigarette smoking ( n = 6 ) , previous pregnancy that exceeded 23 weeks gestation ( n = 4), and inability to contact at follow-up ( n = 7) despite repeated efforts. Forty-four of the participants (32%) were classified as active. All other participants ( n = 93; 68%) were labeled as sedentary. The sample was predominantly white ( n = 112; 82%). Characteristics of the sample are presented in Table 1. Active and sedentary group differences for these characteristics were small. However, the active women had slightly more years (15.9 versus 15.1) of education and had significantly lower prepregnancy BMIs (21.5 versus 23.1) than their sedentary counterparts. The 44 women who were active during pregnancy participated in various types of exercise. These exercises primarily included brisk walking ( n = 33; 75%) and aerobics/exercise class ( n = 15; 34.1%). Participants also were asked to report, via a yes/no question, whether they had exercised three or more times per week during the 6 months before becoming pregnant. Although no prior exercise was reported by 65 (47.4%) of the 137 women, 72 (52.6%) did report exercise of at least three times a week before becoming pregnant. The majority of the participants who were active during pregnancy ( n = 35; 79.5%) also had been active before pregnancy. In the sedentary group, 3 7 (39.8%) had exercised at least three times a week before becoming pregnant. The most frequently cited modes of physical activity are listed in Table 2. The majority ( n = 104; 76%) of the participants had vaginal deliveries, whereas 33 (24%) had cesarean Volume 29, Number 3
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TABLE 2
Type of Exercise Participated in During Pregnancy by the 44 Active Nulliparae Type of Exercise
Vigorous walking Aerobicslexercise class Stair climber Stationary bicycle Jogginghunning Weights Swimming In-line skating Tennis
Number of Women Participating (%) 33 (75.0) 15 (34.1) 9 (20.5) 9 (20.5) 6 (13.6) 4 (9.1) 2 (4.5) 2 (4.5) l(2.3)
deliveries. In the active group, 37 women (84%) delivered vaginally and seven (16%) delivered via cesarean section. While 67 (72%) of the sedentary women delivered vaginally, 26 (28%) required cesarean delivery. Reasons varied for the 33 cesarean deliveries. Primary reasons for cesarean delivery included failure of labor to progress ( n = 12; 36.4%), breech position ( n = 8; 24.3%), and cephalopelvic disproportion ( n = 5; 15.2%). Other reasons ( n = 8; 24.2%) included fetal distress, prolapsed umbilical cord, and the inability to push. No significant differences were found between groups for length of labor, birth weight, maternal
W o m e n who reported regular participation in physical activity during the first
two trimesters of pregnancy were found to be less likely to deliver via cesarean section.
weight gain, or length of gestation. When the data were analyzed by type of delivery, the mean birth weight of the newborns who had been delivered vaginally was 3,416 g (SD = 397) and the mean birth weight of the newborns who had been delivered via cesarean was 3,485 g ( S D = 624). This difference was not significant. The maternal weight gain was similar in both the active and sedentary groups. No significant differences were found between active and sedentary women for the use of epidural anesthesia, other medications, forceps or vacuum extractor devices, episiotomy, or delivery method. The MaylJune 2000
unadjusted odds ratio, however, indicated that the risk of cesarean delivery was 2.05 times greater among sedentary than among active women. Logistic regression, with control for age, BMI change, use of epidural anesthesia, hospital of birth, induced labor, hours of labor, and prepregnancy exercise, demonstrated that the odds of a cesarean delivery were 4.48 (95% confidence interval = 1.2-16.2; p = .023) times greater among sedentary mothers than among active mothers. These results are presented in Table 3.
Discussion Women who reported exercising at least three times per week, for 20 minutes per session, during the first two trimesters of pregnancy were found to be less likely to deliver via cesarean section. The cross-sectional nature of the study design, however, precludes that association from being considered causal. Further study using clinical trials is necessary to demonstrate causality. Using the previously mentioned figure of $3,160 extra cost for each cesarean delivery, it is estimated that
Physicians and nurses can influence pregnant women’s activity patterns through education and encouragement.
potentially an excess of more than $104,000 was spent on the 33 cesarean births in this study. Our estimate of attributable risk, or excess occurrence (incidence of cesarean section in the high-risk group, which in this case is the sedentary group, minus the incidence of cesarean section in the low-risk group, in this case the exercising group) of cesarean section deliveries in the current study is 12 procedures per 100 sedentary women. Thus, approximately 11 (93 x .12) cesarean section deliveries in the current study can potentially be attributed to sedentary behavior. Assuming that all other factors that influence cesarean deliveries are accounted for had these women not been sedentary, medical expenses could have been reduced by $34,760. A portion of the excess costs of cesarean delivery is associated with the longer hospital stays usually required. Zhiwei (1999, with research on births occurring in Utah during 1993, reported that the average hospital stay is 3.56 days for cesarean delivery and 1.59 days for vaginal delivery. The finding of fewer cesarean deliveries among physically active women is in agreement with previous
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TABLE 3
Odds of Cesarean Delivery (N = 13 7)
Variables
odds Ratio
p Value
1.19 4.48 1.17 4.85 1.39 3.37 0.91 1.26
.009 .024 ns ns ns ns ns ns
Age (years) Sedentary during pregnancy BMIa change Epidural Hospital Induced labor Labor hours Prepregnancy exercise
95% Confidence Interval
1.04-1.37 1.23-16.23 0.09-1.51 0.52-44.62 0.33-5.89 0.82-13.94 0.91-1.07 0.45-3.56
aBMI = Body Mass Index.
studies. Zeanah and Schlosser (1993) found that significantly more vaginal deliveries occurred among active women. Using a prospective study design, Hall and Kaufmann (1987) found that 93.3% of women in the most physically active group had vaginal deliveries compared with 71.9% in the least active group. Similarly, Clapp (1990) reported higher rates of vaginal deliveries among physically active women. Efforts are underway to reduce cesarean section delivery rates (Myers & Gleicher, 1988; Socol, Garcia,
P h y s i c a l activi+y may play a role in reducing cesarean section rates.
Peaceman, & Dooley, 1993). A U.S. Department of Health and Human Services (USDHHS)objective, as stated in Healthy People 2000 (1991), is to hold cesarean births to no more than 15% of births by the turn of the century. The overall cesarean rate in this study was 24%. The rate among the physically active group was 15.9%, a figure that approaches the DHHS recommendation. Thus, present data suggest that physical activity may play a role in reducing the number of cesarean sections to the recommended rate. Physical activity is an especially attractive treatment option because it is inexpensive and produces few negative side effects.
Limitations In the current study participants completed a qualitative assessment of physical activity via selfreport. Internal validity of the study may have been increased if more precise methods to measure physical
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activity such as direct observation or movement detection devices had been used. Pate et al. (1995), in their landmark review, reported that in general, the more sound the study design and the more valid the physical activity measurement instruments, the stronger the reported health-related influences of physical activity. Thus, if this study were replicated with more precise physical activity measurement instruments, the positive effect that physical activity asserted on type of delivery may have been affected. Other limitations include the small sample size and lack of verification of birth outcome and exercise behavior. Participant physical activity behavior did, however, resemble national figures that show that 31.2 % of white women living in the United States meet the Centers for Disease Control and Prevention and American College of Sports Medicine physical activity joint recommendation (Jones et al., 1998). Furthermore, in the current study, evidence to attribute 16 cases of cesarean delivery to a particular medical condition (breech, n = 8; fetal distress, prolapsed cord, and the inability to push, n = 8 ) was lacking. No evidence exists, however, that these factors are not related to physical activity and delivery type. Thus, data from these participants were retained in statistical analyses.
Conclusions and Implications The implications of this study suggest that pregnant women should exercise. Nurses and physicians can influence pregnant women's activity patterns through education and encouragement. A physical activity counseling program has been designed by the Centers for Disease Control and Prevention to be delivered by health professionals in the context of an office visit. Topics such as safety, exercise options during bad weather, and overcoming barriers to physical activity are addressed in the curriculum (Patrick et al., 1994). This curriculum is pre-
Volume 29, Number 3
scribed in accordance with the patient’s previous exercise regimen. Women who exercised before becoming pregnant should be encouraged to continue, and those who are sedentary could be motivated to begin exercising. It is important that pregnant women know they may exercise during pregnancy and by doing so could reduce their risk of cesarean section. Researchers (Clapp, 1990; Hall & Kaufmann, 1987; Jackson et al., 1995; Rice & Fort, 1991; Wallace et al., 1986; Zeanah & Schlosser, 1993) indicate that the benefits of regular exercise for the healthy, pregnant woman appear to outweigh the risks. However, some contraindications for exercise do exist during pregnancy. ACOG (1994) offers safety-related recommendations that admittedly do not have a firm basis in randomized clinical trials. The following six medical or obstetric conditions have been identified as contraindications to exercise during pregnancy: pregnancy-induced hypertension, preterm rupture of membranes, preterm labor during a prior or current pregnancy, incompetent cervix, persistent 2nd or 3rd trimester bleeding, or fetal growth restriction. The ACOG recommendations are general in nature. It is suggested that the intensity of exercise should be modified according to maternal symptoms and should not continue to fatigue or exhaustion. Exercise in the supine position should be avoided after the 1st trimester, and caution should be used for those activities that require significant balance. Exercise that involves the potential for even mild abdominal trauma should be avoided. Other recommendations for nutrition, heat dissipation, and resuming physical activity after birth are offered by ACOG (1994). Future suggested research includes replicating the current study with a larger sample that is more ethnically diverse and using more precise physical activity measurement instruments. Additionally, clinical trials could be used to demonstrate causal relationships of different intensities, durations, or modes of physical activity with pregnancy outcomes.
REFERENCES American College of Obstetricians and Gynecologists. (1994). Exercise during pregnancy and the postpartum period ( A C O G Technical Bulletin, 189). Washington, DC: Author. Baddeley, S., & Green, S. (1992). Physical education and the pregnant woman: The way forward. Midwives Chronicle and Nursing Notes, 105(1253), 144-145. Centers for Disease Control and Prevention. (1994). Rates of cesarean delivery-US, 1991. Morbidity and Mortality Weekly Report, 42, 86-89. Clapp, J.F. (1990). The course of labor after endurance exercise during pregnancy. American Journal of Obstetrics and Gynecology, 163, 1799-1805. Gilbert, W.M., Nesbitt, T.S., & Danielson, B. (1999). Child-
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bearing beyond age 40: Pregnancy outcome in 24,032 cases. Obstetrics and Gynecology, 93, 9-14. Hall, D.C., & Kaufmann, D.A. (1987). Effects of aerobic and strength conditioning on pregnancy outcomes. American Journal of Obstetrics and Gynecology, 1.57, 1199-1203. Horns, P.N., Ratcliffe, L.P., Leggett, J.C., & Swanson, M.S. (1996). Pregnancy outcomes among active and sedentary primiparous women. Journal of Obstetric, Gynecologic, and Neonatal Nursing, 25, 49-54. Hosmer, D.W., Taber, S., & Lemeshow, S. (1991). The importance of assessing the fit of logistic regression models: A case study. American Journal of Public Health, 81, 1630-1635. Jackson, M.R., Gott, P., Lye, S.J., Knox-Ritchie, J.W., & Clapp, J.F., 111. (1995). The effects of maternal aerobic exercise on human placental development: Placental volumetric composition and surface areas. Placenta, 16, 179-191. Johnson, R.V. (1994). Mayo Clinic: Complete book of pregnancy and baby’s first year. New York: William Morrow Company. Jones, D.A., Ainsworth, B.E., Croft, J.B., Macera, C.A., Lloyd, E.E., & Yusuf, H.R. (1998). Moderate leisuretime physical activity: Who is meeting the public health recommendations? A national cross-sectional study. Archives of Family Medicine, 7, 285-289. Kulpa, P.J., White, B.M., & Visscher, R. (1987).Aerobic exercise in pregnancy. American Journal of Obstetrics and Gynecology, 156, 1395-1403. Morton, S.C., Williams, M.S., Keeler, E.B., Gambone, J.C., & Kahn, K.L. (1994).Effect of epidural analgesia for labor on the cesarean section rate. Obstetrics and Gynecology, 83, 1045-1052. Myers, S.A., & Gleicher, N. (1988). A successful program to lower cesarean-section rates. N e w England Journal of Medicine, 329, 1511-1516. Pate, R.R., Pratt, M., Blair, S.N., Haskell, W.L., Macera, C.A., Bouchard, C., Buchner, D., Ettinger, W., Heath, G.W., King, A.C., Kriska, A., Leon, A.S., Marcus, B.H., Morris, J., Paffenbarger, R.S., Patrick, K., Pollock, M.L., Rippe, J.M., Sallis, J., & Wilmore, J.H. (1995). Physical activity and public health: A recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine. Journal of the American Medical Association, 2 73, 402-407. Patrick, K., Sallis, J.F., Long, B., Calfas, K.J., Wooten, W., Heath, G., & Pratt, M. (1994). A new tool for encouraging physical activity: Project PACE. Physician and Sportsmedicine, 22, 16-23. Revelli, A., Durando, A., & Massobrio, M. (1992). Exercise and pregnancy: A review of maternal and fetal effects. Obstetrical and Gynecological Survey, 47, 355-367. Rice, P.L., & Fort, I.L. (1991).The relationship of maternal exercise on labor, delivery and health of the newborn. Journal of Sports Medicine and Physical Fitness, 31, 95-99. Socol, M.L., Garcia, P.M., Peaceman, A.M., & Dooley, S.L. (1993). Reducing cesarean births at a primarily private university hospital. American Journal of Obstetrics and Gynecology, 168, 1748-1758.
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Sternfeld, B., Quesenberry, C. P., Eskenazi, B., & Newman, L. A. (1995). Exercise during pregnancy and pregnancy outcome. Medicine and Science in Sports and Exercise, 27, 634-640. U.S. Department of Health and Human Services. (1991). Healthy people 2000: National health promotion and disease prevention objectives (DHHS publication 9150212). Washington, DC: Author. U.S. Department of Health and Human Services. (1996). Physical activity and health: A report of the Surgeon General. Atlanta: Centers for Disease Control and Prevention. Wallace, A.M., Boyer, D.B., Dan, A., & Holm, K. (1986). Aerobic exercise, maternal self-esteem, and physical discomforts during pregnancy. Journal of Nurse-Midwifery, 31, 255-262. Wong, S.C., & McKenzie, D.C. (1987). Cardiorespiratory fitness during pregnancy and its effect on outcome. International Journal of Sports Medicine, 8(2),79-83. Zeanah, M., & Schlosser, S. P. (1993). Adherence to ACOG guidelines on exercise during pregnancy: Effect on pregnancy outcome. Journal of Obstetric, Gynecologic, and Neonatal Nursing, 22, 329-335.
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Zhiwei, L. (1995).Some numbers about delivery in Utah, 1993. Salt Lake City: Utah Office of Health Data Analysis. Retrieved September 1, 1998 from the World Wide Web: http://hlunix.histateat. us/hda/consumer/csection/csectionhml.
Timothy J. Bungum is an assistant professor, Department of Kinesiology, Health Promotion and Recreation, at the University of North Texas in Denton. Dian L. Peaslee is a medical case manager at the CorVel COYporation in Dallas, TX. Allen W Jackson is a professor in the Department of Kinesiology, Health Promotion and Recreation at the University of North Texas in Denton. Miguel A. Perez is an assistant professor in the Department of Health Sciences, California State University-Fresno. Address for cowespondence: Timothy J. Bungum, DrPH, CHES, RO. Box 311337, Dept. KHPR, University of North Texas, Denton, TX 76201-1337. E-mail: bungum@coefs. coe.unt.edu.
Volume 29, Number 3
C L ~ I - I C ASTUDIES L,
Exercise During Pregnancy and Type of Delive y in Nulliparae T i m o t h y J. B u n g u m , DrPH, CHES, Dian L. Peaslee, RN, BAN, MS, Allen I% Jackson, EdD, Miguel A. Perez, PhD, CHES
=
Objective: To assess the association between participation in aerobic exercise during the first two trimesters of pregnancy and type of delivery in nulliparous women. Design: Nonexperimental, retrospective. Setting: A large metropolitan area in the southwestern United States. Participants: 137 nulliparous women. Outcome Measures: Method of delivery. Results: An unadjusted odds ratio showed that sedentary women ( n = 93) were 2.05 times more likely to deliver via cesarean section than active women ( n = 44), but this relationship was not statistically significant. Through logistic regression analysis with control for the mother's prepregnancy exercise program, age, use of epidural anesthesia, change in prepregnancy to delivery body mass index, labor length, whether labor was induced, and the hospital of birth, the odds of cesarean delivery were found to be 4.5 times greater for sedentary women than for active women. Conclusion: Regular participation in physical activity during the first two trimesters of pregnancy may be associated with reduced risk for cesarean delivery in nulliparous women. JOG" 29,
250-264; 2000. Keywords: ExerciseNul Iiparuepregnancy Accepted: September 1 999
The potential benefits of physical activity are well known (U.S. Department of Health and Human Services, 1996). Pregnant women often are advised to exercise but should not do so to the point of exhaustion. Exercise in certain positions and any activity that involves the potential for
258 JOG"
abdominal trauma should be avoided. The focus of this article is the relationship between physical activity during the first two trimesters of pregnancy and type of delivery.
Literature Review In recent decades pregnant women have become more likely to engage in exercise (Baddeley & Green, 1992; Wallace, Boyer, Dan, & Holm, 1986). Accordingly, health professionals have investigated the risks and benefits of exercise during pregnancy. Revelli, Durando, and Massobrio (1992) suggest that exercise benefits most healthy pregnant women who were physically active prior to conception. Three studies have shown that women can engage in aerobic exercise during healthy pregnancies without compromising fetal growth and development or complicating the processes of pregnancy, labor, or delivery (Hall & Kaufmann, 1987; Jackson, Gott, Lye, KnoxRitchie, & Clapp, 1995; Rice & Fort, 1991). Potential benefits of exercise during pregnancy include a decrease in pregnancy-related discomforts (Horns, Ratcliffe, Leggett, & Swanson, 1996; Sternfield, Quesenberry, Eskenazi, & Newman, 1995; Wallace et al., 1986), shortened labor (Kulpa, White, & Visscher, 1987; Wong & McKenzie, 1987), and perhaps an increase in the likelihood of vaginal delivery. Two studies have demonstrated a higher incidence of vaginal delivery among women who exercise (Clapp, 1990; Hall & Kaufmann, 1987). Clapp (1990), using a prospective study design, showed that women who exercised throughout their pregnancies had higher rates of vaginal births (88%) than women Volume 29, Number 3
who discontinued their exercise regimen by the end of their 1st trimester (70%). Hall and Kaufmann (1987) assessed data from 845 women who were given the option of participating in a prenatal program that involved stretching exercise and aerobic workouts on stationary bicycles. Those who participated in the most exercise sessions during pregnancy delivered vaginally in 93% of cases, while those who exercised the least delivered vaginally 71% of the time. The reasons exercise would influence type of delivery are not clear. It is hypothesized that increased or maintained fitness during pregnancy allows the mother to better manage the rigors of childbirth. Vaginal deliveries are generally preferred to cesarean sections because the risks to the mother for a cesarean delivery include infection, excessive blood loss, decreased bowel function, respiratory complications, reactions to anesthesia, longer hospital stays, and longer recovery periods (Johnson, 1994). Another benefit of vaginal rather than cesarean delivery is the lower medical cost. In 1994, delivery via cesarean section cost $3,160 more than a vaginal delivery (Centers for Disease Control and Prevention, 1994). Therefore, vaginal deliveries, when possible, are preferable to cesarean deliveries. Virtually all researchers who have assessed the effects of physical activity on delivery type have included women who have completed one or more pregnancies. In addition to parity, age (Gilbert, Nesbitt, & Danielson, 1999) and the use of epidural anesthesia during labor (Morton, Williams, Keeler, Gambone, & Kahn, 1994) have been shown to influence delivery type. It also has been suggested that hospital of birth may influence type of delivery. Because previous pregnancy has been shown to influence type of delivery (Gilbert et al., 1999), the current study included only women who had not completed a pregnancy past 23 weeks of gestation (i.e., nulliparae). The purpose of this investigation was to assess differences in rates of cesarean versus vaginal delivery among women who were physically active during the first two trimesters of their pregnancy and those who were not. A secondary objective was to investigate the association of maternal physical activity during pregnancy and newborn birth weight.
Method Participants Participants were nulliparous women who attended hospital-based childbirth education classes or a private fitness center that offered a prenatal aerobic exercise program. The childbirth education classes were offered at three private, for-profit, hospitals. These childbirth education classes met weekly for 6 weeks. Class sessions typically occurred 2-4 weeks before the
Mayl’une 2000
anticipated delivery. One of the authors (D.P.) attended the final childbirth education class session of three classes to request participants for the study. Women who were willing to participate signed an informed consent statement that explained the study’s procedures and potential risks associated with involvement. Approval to conduct the research was obtained from the participating university’s institutional review board and a similar board at each hospital. The owner of the private fitness center agreed to allow participants in the prenatal exercise class the option to participate in this project. Participants were residents of a large metropolitan area in the southwestern United States. In addition to the requirement of nulliparity, criteria for study inclusion mandated that the women be nonsmokers, expecting a singleton birth, and age 17-40 years at the time of delivery. Further, participants must have been free of gestational diabetes, preeclampsia, high blood pressure, and abnormal bleeding during the pregnancy. Participants also were asked about other pregnancy-related problems. Data were collected over an 8-week period during the spring of 1997. A checklist was used to measure physical activity. Participants self-reported the average number of times they had engaged in selected physical activities at least three times per week, for at least 20 minutes during each trimester of pregnancy. The physical activity checklist included the following activities: swimming, brisk walking, running/jogging, aerobic dance, stationary or regular bicycling, stairclimber work, racquet sports, in-line skating, and other. Women who reported regular physical activity (three or more sessions of 20 minutes or more per week) during the 1st and 2nd trimesters were labeled active. All other women were classified as sedentary. These guidelines were selected because they are similar to those recommended by the American College of Obstetricians and Gynecologists (ACOG) (1994).
Procedure Initial data were collected before the delivery, and a follow-up phone call was made approximately 2 weeks after the expected delivery date. The first data collection involved participant completion of a 3 1-item written survey. This survey produced, in addition to the previously mentioned vaiiables, information regarding the mother’s age, ethnic background, marital status, a brief medical history, and anticipated due date. A pilot test of the survey instrument was administered to seven women who had recently delivered healthy newborns. The goal of the pilot study was to identify items that were unclear or difficult to comprehend. Data from these women were not included in subsequent analyses. Only minor changes were made to the questionnaire as a result of these women’s feedback.
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TABLE 1
Characteristics of 137 Nulliparae in the Active and Sedentary Groups Variables
Age (years) Education (years) Prepregnant weight (Ib) Prepregnant body mass indexes Body mass index change Height (cm)
Active (M f SD)
Sedentay (M SD)
29.6 t 3.3 15.9 * 1.5 130.4 21.5 21.5 * 3.1 5.61 t 1.5 165.9 * 6.2
28.4 t 4.6 15.1 t 1.7 138.9 t 26.3 23.1 t 3.85 5.94 t 2.1 165.4 t 6.4
During the follow-up telephone call, mothers were asked the date of birth, birth weight, gender, the number of weeks of gestation, the mother's weight at the last check-up before giving birth, whether the labor had been induced, whether an episiotomy had been performed, whether forceps or a vacuum extractor had been used, whether an epidural had been administered, and the method of birth (vaginal or cesarean). A reminder card that listed the information that would be requested during this follow-up phone call was provided at the time the participants were recruited. Accordingly, most participants were expecting the follow-up phone call and readily reported the requested data. No review of records or follow-up calls were made to assess the reliability or validity of this data. All deliveries occurred in hospital settings under the care of a physician.
Data Analysis Descriptive statistics were calculated for all variables. The t test was used to identify differences between the active and sedentary groups. Maternal characteristics of age, education, and body mass index (BMI) were analyzed for differences between the two groups. An unadjusted odds ratio that assessed the likelihood of having a cesarean section or vaginal delivery was calculated for the two groups. A multiple logistic regression analysis was used with control for the following factors: mother's physical activity level before pregnancy, mother's age, change in prepregnancy to predelivery BMI, use of epidural anesthesia, labor length, whether labor was induced, and the hospital of birth. In this way, the odds of delivery via cesarean for active versus sedentary women were determined. These particular factors were accounted for because they have been shown to influence type of delivery. Prepregnancy exercise was controlled for to isolate the effects of exercise during pregnancy. Controlling for these variables produced an odds ratio free of the influence of major extra-
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*
t
Value 1.75 2.79 2.00 5.61 0.96 .39
p
.08 .006 .05 .02 ns ns
neous variation related to type of delivery. A goodness of fit test (Hosmer, Taber, & Lemeshow, 1991) indicated that the model fit the data adequately, p = ns.
Results A total of 164 women volunteered for the study, and data were analyzed for 137. Reasons for exclusions included the presence of diabetes ( n = l o ) , cigarette smoking ( n = 6 ) , previous pregnancy that exceeded 23 weeks gestation ( n = 4), and inability to contact at follow-up ( n = 7) despite repeated efforts. Forty-four of the participants (32%) were classified as active. All other participants ( n = 93; 68%) were labeled as sedentary. The sample was predominantly white ( n = 112; 82%). Characteristics of the sample are presented in Table 1. Active and sedentary group differences for these characteristics were small. However, the active women had slightly more years (15.9 versus 15.1) of education and had significantly lower prepregnancy BMIs (21.5 versus 23.1) than their sedentary counterparts. The 44 women who were active during pregnancy participated in various types of exercise. These exercises primarily included brisk walking ( n = 33; 75%) and aerobics/exercise class ( n = 15; 34.1%). Participants also were asked to report, via a yes/no question, whether they had exercised three or more times per week during the 6 months before becoming pregnant. Although no prior exercise was reported by 65 (47.4%) of the 137 women, 72 (52.6%) did report exercise of at least three times a week before becoming pregnant. The majority of the participants who were active during pregnancy ( n = 35; 79.5%) also had been active before pregnancy. In the sedentary group, 3 7 (39.8%) had exercised at least three times a week before becoming pregnant. The most frequently cited modes of physical activity are listed in Table 2. The majority ( n = 104; 76%) of the participants had vaginal deliveries, whereas 33 (24%) had cesarean Volume 29, Number 3
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TABLE 2
Type of Exercise Participated in During Pregnancy by the 44 Active Nulliparae Type of Exercise
Vigorous walking Aerobicslexercise class Stair climber Stationary bicycle Jogginghunning Weights Swimming In-line skating Tennis
Number of Women Participating (%) 33 (75.0) 15 (34.1) 9 (20.5) 9 (20.5) 6 (13.6) 4 (9.1) 2 (4.5) 2 (4.5) l(2.3)
deliveries. In the active group, 37 women (84%) delivered vaginally and seven (16%) delivered via cesarean section. While 67 (72%) of the sedentary women delivered vaginally, 26 (28%) required cesarean delivery. Reasons varied for the 33 cesarean deliveries. Primary reasons for cesarean delivery included failure of labor to progress ( n = 12; 36.4%), breech position ( n = 8; 24.3%), and cephalopelvic disproportion ( n = 5; 15.2%). Other reasons ( n = 8; 24.2%) included fetal distress, prolapsed umbilical cord, and the inability to push. No significant differences were found between groups for length of labor, birth weight, maternal
W o m e n who reported regular participation in physical activity during the first
two trimesters of pregnancy were found to be less likely to deliver via cesarean section.
weight gain, or length of gestation. When the data were analyzed by type of delivery, the mean birth weight of the newborns who had been delivered vaginally was 3,416 g (SD = 397) and the mean birth weight of the newborns who had been delivered via cesarean was 3,485 g ( S D = 624). This difference was not significant. The maternal weight gain was similar in both the active and sedentary groups. No significant differences were found between active and sedentary women for the use of epidural anesthesia, other medications, forceps or vacuum extractor devices, episiotomy, or delivery method. The MaylJune 2000
unadjusted odds ratio, however, indicated that the risk of cesarean delivery was 2.05 times greater among sedentary than among active women. Logistic regression, with control for age, BMI change, use of epidural anesthesia, hospital of birth, induced labor, hours of labor, and prepregnancy exercise, demonstrated that the odds of a cesarean delivery were 4.48 (95% confidence interval = 1.2-16.2; p = .023) times greater among sedentary mothers than among active mothers. These results are presented in Table 3.
Discussion Women who reported exercising at least three times per week, for 20 minutes per session, during the first two trimesters of pregnancy were found to be less likely to deliver via cesarean section. The cross-sectional nature of the study design, however, precludes that association from being considered causal. Further study using clinical trials is necessary to demonstrate causality. Using the previously mentioned figure of $3,160 extra cost for each cesarean delivery, it is estimated that
Physicians and nurses can influence pregnant women’s activity patterns through education and encouragement.
potentially an excess of more than $104,000 was spent on the 33 cesarean births in this study. Our estimate of attributable risk, or excess occurrence (incidence of cesarean section in the high-risk group, which in this case is the sedentary group, minus the incidence of cesarean section in the low-risk group, in this case the exercising group) of cesarean section deliveries in the current study is 12 procedures per 100 sedentary women. Thus, approximately 11 (93 x .12) cesarean section deliveries in the current study can potentially be attributed to sedentary behavior. Assuming that all other factors that influence cesarean deliveries are accounted for had these women not been sedentary, medical expenses could have been reduced by $34,760. A portion of the excess costs of cesarean delivery is associated with the longer hospital stays usually required. Zhiwei (1999, with research on births occurring in Utah during 1993, reported that the average hospital stay is 3.56 days for cesarean delivery and 1.59 days for vaginal delivery. The finding of fewer cesarean deliveries among physically active women is in agreement with previous
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TABLE 3
Odds of Cesarean Delivery (N = 13 7)
Variables
odds Ratio
p Value
1.19 4.48 1.17 4.85 1.39 3.37 0.91 1.26
.009 .024 ns ns ns ns ns ns
Age (years) Sedentary during pregnancy BMIa change Epidural Hospital Induced labor Labor hours Prepregnancy exercise
95% Confidence Interval
1.04-1.37 1.23-16.23 0.09-1.51 0.52-44.62 0.33-5.89 0.82-13.94 0.91-1.07 0.45-3.56
aBMI = Body Mass Index.
studies. Zeanah and Schlosser (1993) found that significantly more vaginal deliveries occurred among active women. Using a prospective study design, Hall and Kaufmann (1987) found that 93.3% of women in the most physically active group had vaginal deliveries compared with 71.9% in the least active group. Similarly, Clapp (1990) reported higher rates of vaginal deliveries among physically active women. Efforts are underway to reduce cesarean section delivery rates (Myers & Gleicher, 1988; Socol, Garcia,
P h y s i c a l activi+y may play a role in reducing cesarean section rates.
Peaceman, & Dooley, 1993). A U.S. Department of Health and Human Services (USDHHS)objective, as stated in Healthy People 2000 (1991), is to hold cesarean births to no more than 15% of births by the turn of the century. The overall cesarean rate in this study was 24%. The rate among the physically active group was 15.9%, a figure that approaches the DHHS recommendation. Thus, present data suggest that physical activity may play a role in reducing the number of cesarean sections to the recommended rate. Physical activity is an especially attractive treatment option because it is inexpensive and produces few negative side effects.
Limitations In the current study participants completed a qualitative assessment of physical activity via selfreport. Internal validity of the study may have been increased if more precise methods to measure physical
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activity such as direct observation or movement detection devices had been used. Pate et al. (1995), in their landmark review, reported that in general, the more sound the study design and the more valid the physical activity measurement instruments, the stronger the reported health-related influences of physical activity. Thus, if this study were replicated with more precise physical activity measurement instruments, the positive effect that physical activity asserted on type of delivery may have been affected. Other limitations include the small sample size and lack of verification of birth outcome and exercise behavior. Participant physical activity behavior did, however, resemble national figures that show that 31.2 % of white women living in the United States meet the Centers for Disease Control and Prevention and American College of Sports Medicine physical activity joint recommendation (Jones et al., 1998). Furthermore, in the current study, evidence to attribute 16 cases of cesarean delivery to a particular medical condition (breech, n = 8; fetal distress, prolapsed cord, and the inability to push, n = 8 ) was lacking. No evidence exists, however, that these factors are not related to physical activity and delivery type. Thus, data from these participants were retained in statistical analyses.
Conclusions and Implications The implications of this study suggest that pregnant women should exercise. Nurses and physicians can influence pregnant women's activity patterns through education and encouragement. A physical activity counseling program has been designed by the Centers for Disease Control and Prevention to be delivered by health professionals in the context of an office visit. Topics such as safety, exercise options during bad weather, and overcoming barriers to physical activity are addressed in the curriculum (Patrick et al., 1994). This curriculum is pre-
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scribed in accordance with the patient’s previous exercise regimen. Women who exercised before becoming pregnant should be encouraged to continue, and those who are sedentary could be motivated to begin exercising. It is important that pregnant women know they may exercise during pregnancy and by doing so could reduce their risk of cesarean section. Researchers (Clapp, 1990; Hall & Kaufmann, 1987; Jackson et al., 1995; Rice & Fort, 1991; Wallace et al., 1986; Zeanah & Schlosser, 1993) indicate that the benefits of regular exercise for the healthy, pregnant woman appear to outweigh the risks. However, some contraindications for exercise do exist during pregnancy. ACOG (1994) offers safety-related recommendations that admittedly do not have a firm basis in randomized clinical trials. The following six medical or obstetric conditions have been identified as contraindications to exercise during pregnancy: pregnancy-induced hypertension, preterm rupture of membranes, preterm labor during a prior or current pregnancy, incompetent cervix, persistent 2nd or 3rd trimester bleeding, or fetal growth restriction. The ACOG recommendations are general in nature. It is suggested that the intensity of exercise should be modified according to maternal symptoms and should not continue to fatigue or exhaustion. Exercise in the supine position should be avoided after the 1st trimester, and caution should be used for those activities that require significant balance. Exercise that involves the potential for even mild abdominal trauma should be avoided. Other recommendations for nutrition, heat dissipation, and resuming physical activity after birth are offered by ACOG (1994). Future suggested research includes replicating the current study with a larger sample that is more ethnically diverse and using more precise physical activity measurement instruments. Additionally, clinical trials could be used to demonstrate causal relationships of different intensities, durations, or modes of physical activity with pregnancy outcomes.
REFERENCES American College of Obstetricians and Gynecologists. (1994). Exercise during pregnancy and the postpartum period ( A C O G Technical Bulletin, 189). Washington, DC: Author. Baddeley, S., & Green, S. (1992). Physical education and the pregnant woman: The way forward. Midwives Chronicle and Nursing Notes, 105(1253), 144-145. Centers for Disease Control and Prevention. (1994). Rates of cesarean delivery-US, 1991. Morbidity and Mortality Weekly Report, 42, 86-89. Clapp, J.F. (1990). The course of labor after endurance exercise during pregnancy. American Journal of Obstetrics and Gynecology, 163, 1799-1805. Gilbert, W.M., Nesbitt, T.S., & Danielson, B. (1999). Child-
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bearing beyond age 40: Pregnancy outcome in 24,032 cases. Obstetrics and Gynecology, 93, 9-14. Hall, D.C., & Kaufmann, D.A. (1987). Effects of aerobic and strength conditioning on pregnancy outcomes. American Journal of Obstetrics and Gynecology, 1.57, 1199-1203. Horns, P.N., Ratcliffe, L.P., Leggett, J.C., & Swanson, M.S. (1996). Pregnancy outcomes among active and sedentary primiparous women. Journal of Obstetric, Gynecologic, and Neonatal Nursing, 25, 49-54. Hosmer, D.W., Taber, S., & Lemeshow, S. (1991). The importance of assessing the fit of logistic regression models: A case study. American Journal of Public Health, 81, 1630-1635. Jackson, M.R., Gott, P., Lye, S.J., Knox-Ritchie, J.W., & Clapp, J.F., 111. (1995). The effects of maternal aerobic exercise on human placental development: Placental volumetric composition and surface areas. Placenta, 16, 179-191. Johnson, R.V. (1994). Mayo Clinic: Complete book of pregnancy and baby’s first year. New York: William Morrow Company. Jones, D.A., Ainsworth, B.E., Croft, J.B., Macera, C.A., Lloyd, E.E., & Yusuf, H.R. (1998). Moderate leisuretime physical activity: Who is meeting the public health recommendations? A national cross-sectional study. Archives of Family Medicine, 7, 285-289. Kulpa, P.J., White, B.M., & Visscher, R. (1987).Aerobic exercise in pregnancy. American Journal of Obstetrics and Gynecology, 156, 1395-1403. Morton, S.C., Williams, M.S., Keeler, E.B., Gambone, J.C., & Kahn, K.L. (1994).Effect of epidural analgesia for labor on the cesarean section rate. Obstetrics and Gynecology, 83, 1045-1052. Myers, S.A., & Gleicher, N. (1988). A successful program to lower cesarean-section rates. N e w England Journal of Medicine, 329, 1511-1516. Pate, R.R., Pratt, M., Blair, S.N., Haskell, W.L., Macera, C.A., Bouchard, C., Buchner, D., Ettinger, W., Heath, G.W., King, A.C., Kriska, A., Leon, A.S., Marcus, B.H., Morris, J., Paffenbarger, R.S., Patrick, K., Pollock, M.L., Rippe, J.M., Sallis, J., & Wilmore, J.H. (1995). Physical activity and public health: A recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine. Journal of the American Medical Association, 2 73, 402-407. Patrick, K., Sallis, J.F., Long, B., Calfas, K.J., Wooten, W., Heath, G., & Pratt, M. (1994). A new tool for encouraging physical activity: Project PACE. Physician and Sportsmedicine, 22, 16-23. Revelli, A., Durando, A., & Massobrio, M. (1992). Exercise and pregnancy: A review of maternal and fetal effects. Obstetrical and Gynecological Survey, 47, 355-367. Rice, P.L., & Fort, I.L. (1991).The relationship of maternal exercise on labor, delivery and health of the newborn. Journal of Sports Medicine and Physical Fitness, 31, 95-99. Socol, M.L., Garcia, P.M., Peaceman, A.M., & Dooley, S.L. (1993). Reducing cesarean births at a primarily private university hospital. American Journal of Obstetrics and Gynecology, 168, 1748-1758.
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Sternfeld, B., Quesenberry, C. P., Eskenazi, B., & Newman, L. A. (1995). Exercise during pregnancy and pregnancy outcome. Medicine and Science in Sports and Exercise, 27, 634-640. U.S. Department of Health and Human Services. (1991). Healthy people 2000: National health promotion and disease prevention objectives (DHHS publication 9150212). Washington, DC: Author. U.S. Department of Health and Human Services. (1996). Physical activity and health: A report of the Surgeon General. Atlanta: Centers for Disease Control and Prevention. Wallace, A.M., Boyer, D.B., Dan, A., & Holm, K. (1986). Aerobic exercise, maternal self-esteem, and physical discomforts during pregnancy. Journal of Nurse-Midwifery, 31, 255-262. Wong, S.C., & McKenzie, D.C. (1987). Cardiorespiratory fitness during pregnancy and its effect on outcome. International Journal of Sports Medicine, 8(2),79-83. Zeanah, M., & Schlosser, S. P. (1993). Adherence to ACOG guidelines on exercise during pregnancy: Effect on pregnancy outcome. Journal of Obstetric, Gynecologic, and Neonatal Nursing, 22, 329-335.
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Zhiwei, L. (1995).Some numbers about delivery in Utah, 1993. Salt Lake City: Utah Office of Health Data Analysis. Retrieved September 1, 1998 from the World Wide Web: http://hlunix.histateat. us/hda/consumer/csection/csectionhml.
Timothy J. Bungum is an assistant professor, Department of Kinesiology, Health Promotion and Recreation, at the University of North Texas in Denton. Dian L. Peaslee is a medical case manager at the CorVel COYporation in Dallas, TX. Allen W Jackson is a professor in the Department of Kinesiology, Health Promotion and Recreation at the University of North Texas in Denton. Miguel A. Perez is an assistant professor in the Department of Health Sciences, California State University-Fresno. Address for cowespondence: Timothy J. Bungum, DrPH, CHES, RO. Box 311337, Dept. KHPR, University of North Texas, Denton, TX 76201-1337. E-mail: bungum@coefs. coe.unt.edu.
Volume 29, Number 3