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Nonspecific date of last menstrual period
Nonspecific date of last menstrual period An
indication
of
WALDEMAR E.
H.
BERT
Seattle,
YOUNG,
poor
reproductive
WENNER,
outcome
M.D.
B.A.
Washington
Socially disadvantaged women whose medical records showed they reported nonspecific last menstrual period dates at the first prenatal visit had a disproportionately high incidence of complications in reproduction. The complications included an increased likelihood of delivery by cesarean section and lighter, more immature infants. Nonspecific last menstrual periods were also associated with indicators of increased risk available early in pregnancy. The increased number of complications among disadvantaged women with nonspecific last menstrual period dates was not explained by prenatal vaginal bleeding or irregular menstrual periods. A possible explanation for the association appeared to be the social circumstances. Mothers who reported nonspecific last menstrual period dates tended to be mothers with more disadvantaged social circumstances. These circumstances have been found to be associated with poor reproductive outcome.
T H E A B I L I T Y to anticipate problems is crucial in providing quality medical care to large numbers of pregnant women and their offspring. Improvement of this ability through the use of systematic risk assessment procedures has been previously explored.ll 2 IdentiFrom the Department the Child Development Retardation Center, Washington.
of Pediatrics
fication of “at-risk” patients can provide a basis for the allocation of appropriate health and social services and, concomitantly, can decrease to appropriate levels the intensity of surveillance for problems in the general population.3p 4 Risk identification has had varying degrees of sophistication, ranging from simple listing of individual indicators of poor outcome to compilations that weigh a multitude of indicators relative to their combined impact on outcome. 5l 6 Two means of improving the identification of “at-risk” patients are: ( 1) demonstration of previously unrecognized or undervalued factors or procedures indicating increased risk, and (2) elucidation of the interrelationships of risk factors. In an effort to improve the identification of “at-risk” infants, medical and social information was examined in a cohort of 357 infants. This information had been considered in clinical decisions about the inclusion of perinates in a high-risk infant followup program. Among the factors considered was maternal uncertainty about the specific date of the last menstrual period. Initially, this factor was included because of interest
and
and Mental University of
Supported by a grant from the Washinaton Association for Retarded Children Trust Fund; by Project No. 913, Maternal and Child Health Service, Health Services and Mental Health Administration, Department of Health, Education, and Welfare; by Grant No. HO02274 from the National Institute of Child Health and Human Development, National Institutes of Health, Department of Health, Education, and Welfare; and by Contract No. N.I.H. 71-4174, Division of Nursing, National Institutes of Health, Department of Health, Education, and Welfare. Received 1974. Revised Accepted
for publication April May
27,
January
15,
1974.
8, 1974.
Reprint requests: Dr. Waldemar Wenner, SC-74, University of Washington, Seattle, Washington
H. 98195. 1071
1072
Wenner
and Young
in information pertinent to the determination of gestational age and prematurity, themselves factors of central interest. However, a strong tendency was found for mothers who reported nonspecific last menstrual period dates to have given birth to infants who were considered “high risk.” Of infants on whom a “risk” decision was made, 66 per cent whose mothers reported nonspecific last menstrual periods were enrolled in the high risk follow-up program; only 38 per cent of infants born to mothers with specific last menstrual period dates were enrolled (chi square = 22.696; degrees of freedom = 1; p < 0.001). This was unexpected because last menstrual period date “specificity” was not among the decision criteria which included a variety of medical and psychosocial factors. This association of last menstrual period specificity with clinical decisions concerning probable risk suggested that last menstrual period specificity itself deserved examination as an indicator of increased risk. Questions to be answered by this inquiry were: ( 1) Is lack of last menstrual period specificity associated with increased risk of poor maternal and fetal outcome? (2) What are the relationships of last menstrual period specificity to risk indicators which can be obtained early in pregnancy? Method
Subjects. Infants whose mothers receive prenatal care at University Hospital under the auspices of the Seattle-King County Health Department’s Maternal and Infant Care Program are referred for pediatric care to the Child Development and Mental Retardation Center unless they are relinquished for adoption or die prior to referral. To be eligible for this program, at the time of enrollment the mothers must reside in certain areas of Seattle with high infant morbidity and mortality rates. Between July 1, 1969, and June 30, 1970, 357 infants were referred. The mothers tended to be young (median age, 19.86 years, mean age, 21.14 years), urban, of low social position (66 per cent of heads of household in Hollingshead’s7 Class
Am.
December J. Obstet.
15, 1974 Gynecol.
V and an additional 24 per cent in Class IV), often primiparous (57 per cent), and single (29 per cent). Among the multiparous women, 41 per cent were having their second pregnancy; 24 per cent, their third; and 15 per cent their fourth. The racial and cultural backgrounds were mixed (54 per cent white, 37 per cent black, 9 per cent Native American, Eskimo, Chicano, and Oriental). Mothers were placed in the “specific” last menstrual period group (No. = 235) if their records showed that a date, specific to the day, for the start of the last menstrual period was reported at the initial visit to the obstetrician. Mothers who did not report a specific date were placed in the “nonspecific” last menstrual period group (No. = 120) . Nonspecific last menstrual period date entries included early-, middle-, or late-month entries, specific only to the week, no entry when the rest of the obstetric history was present, and notation of “unknown” or “questionable.” Data collection. The information was tabulated from maternal and infant medical records and from a demographic record completed by the mother at the infant’s first pediatric visit. Professional staff compiling the records included nutritionists, physicians, public health nurses, and social workers. Data were taken from the charts by 4 trained coders whose interobserver reliability was maintained at the 95 per cent level of agreement for all variables. They used a coding manual developed for this population. It defined each of the variables in mutually exclusive and exhaustive categories, rankings, or intervals. Inconsistencies in the record were treated as missing information. The accuracy of the information found in the medical record could, of course, not be controlled for. It was assumed to be acceptable for use in this exploratory study. A separate analysis of the relative amounts of missing information in each of the two last menstrual period groups failed to show that either group was more prone to have missing information. Some variables were combined and some categorizations were collapsed for analysis.
Volume Number
120 8
Nonspecific
Table I. Maternal
and fetal outcome
proteinuria Specific LMP
Prenatal
Nonspecific Delivery
>
compared
Nonspecific
5
Nonspecific
10.0
x2
117
“1.4
df= P -=C
7.481 1 0.01
226
1.8
119
a.4
x2 x df= i P -=C
9.180 1 0.005
“34
15.4
x2 z.z df=
120
29.2
8.557 1 0.005
a$neic
231
0.9
x’
df= P -C
4.467 1 0.05
I
i
=
section
6
LMP
or more
in two groups
230
Specific LMP One
1073
trace
LMP
Apgar
period
%
Specific LMP I Minute
menstrual
No.
LMP
by cesarean
last
i
P
.<
episodes
Specific LMP
Ez
Nonspecific LMP muscle tone abnormality Specific LMP
119
5.0
i
230
1.7
Nonspecific
118
7.6
x2 zzz df= i P <
5.970 1 0.025
Specific LMP
232
10.3
Nonspecific
119
20.2
x2 = df= i P <
5.624 1 0.02.5
233
2.1
119
9.2
x2 = df= i P <
7.583 1 0.01
Specific LMP
232
3,294.27* rt 539.6
Nonspecific
115
3,111.12* + 594.7
Infant
Infant
LMP
hospital
Gavage-fed
stay
>
4 days
LMP infant
Specific LMP Nonspecific Infant
birth
LMP weight
(singletons)
LMP
LMP = Last menstrual period. *Mean
I ! standard
tOne-tailed
deviation
in
df
=
Degrees
t = 2.08 df = 345 0.002t P = .-
of freedom.
grams.
test.
Results
Association of last menstrual period specificity with poor reproductive outcome. To determine whether mothers who reported nonspecific last menstrual period dates were at increased risk of poor maternal and fetal outcome, 23 variables relating to complications of the pregnancy, delivery, or hospital course of the newborn infant were examined. Some possible complications such as neonatal convulsions had veri low or absent occurrence rates in this cohort and, therefore, were not examined. The following significant associations were found (Table I) : Women in the nonspecific group were almost 5 times as likely to be
delivered by cesarean section. The proportion of cesarean sections occasioned by a previous cesarean section was approximately equal in the two groups, 25 per cent in the “exact” group and 30 per cent in the “nonspecific” group. The reasons for primary cesarean sections in both groups included: relative cephalopelvic disproportion (4 cases), failure of progression of labor (3 cases), cord prolapse (1 case), and fetal distress (1 cltsej. The mean birth weight of singleton infants whose mothers reported a nonspecific last menstrual period was 3,111 grams, 183 grams less than that of infants born to women reporting a specific last menstrual period. Accompanying the birth weight dif-
1074
Wenner
and
Young Am.
ference were other suggestions of an increased incidence of immature infants: Gavage feeding and apneic episodes were approximately 5 times greater; abnormalities of muscle tone (either hyper- or hypo-tonus was noted at least twice while the infant was in the newborn nursery) were about 4vz times more frequent; twice as many of the infants of mothers in the nonspecific group stayed in the hospital longer than 4 days; the mean duration of hospitalization was 5.2 days, almost 2 days longer than infants born to mothers with exact last menstrual periods. Determination of the relation of size to gestational age is difficult to interpret because of questions about gestational age in the nonspecific last menstrual period group. This relationship is not reported for that reason. Proteinuria greater than trace was twice as frequent in the nonspecific last menstrual period group of pregnancies. Infants of women with nonspecific last menstrual periods had 1 minute Apgar scores of 6 or less almost twice as often. For both primiparous and multiparous women, the proportion with nonspecific last menstrual period dates approximated one third. The pregnancy outcome variables found to be significantly associated with last menstrual period specificity status and enumerated above almost all showed a greater occurrence of poor outcome if a woman reported a nonspecific last menstrual period, whether the mother was having the first or a subsequent pregnancy. The exception was the variable “duration of hospital stay of the infant after birth”; the infants of multiparas with specific last menstrual periods stayed a nonsignificant one tenth of a day longer than those of nonspecific last menstrual period multiparas. Only associations within the primiparous subsample, and not all of these, maintained statistical significance when the total cohort was subdivided according to parity. The remaining 15 variables included hyperemesis gravidarum, prenatal vaginal bleeding, prenatal urinary tract infection, maternal hypertension, use of magnesium
December J. Obstet.
15, 1974 Gynecol.
sulfate during labor and delivery, use of indicated forceps, duration of the second stage of labor, abnormalities of the fetal heart rate during labor or delivery, meconium staining of the amniotic fluid, 5 minute Apgar scores below 6, infant temperatures below 36’ C. following a recording above that level, number of instances of infant jitteriness, hours elapsing after birth before infants who were not gavage fed were reported to have taken two successive feedings well, cyanosis with feedings, and congenital anomalies. Among these variables where significant associations were not found in the entire sample, the nonspecific last menstrual period group contained a greater proportion of individuals having complications in 10. Thus, in 78 per cent of all the variables examined in the entire cohort, there was a greater proportion of individuals with poor outcome in the nonspecific last menstrual period group. This was also true in the multiparous subsample. This proportion increased to 83 per cent among the primiparous subsample. However, first-time mothers showed a significantly increased incidence of both abnormalities of the fetal heart during labor and the use of indicated forceps if they reported specific last menstrual periods. These two were the only significant associations among the 69 examined that were contrary to the hypothesis that women who report nonspecific last menstrual period dates tend to have an increased incidence of poor reproductive outcome.
Relationship of last menstrual period specificity to known risk indicators. The relationships of last menstrual period specificity to other risk characteristics available early in pregnancy were determined by examining 15 variables relating to maternal prepregnancy medical status, to demographic descriptors of the mother, and to social conditions that might influence the mother and her offspring. The following significant associations were found (Table II) : The mothers’ reports of their nonpregnant weight showed the nonspecific last menstrual period group to be 7 pounds lighter. The difference
Volume Number
120 8
Nonspecific
Table II. Medical,
demographic,
and social risk indicators
compared
Specific Indicator
No.
Maternal education Beyond high school Completed high school or age-appropriate Did not complete high school or grade age level Maternal age Less than 20 years 20 to 34 years Greater than 34 years Marital status at delivery Married Single Other (widowed, divorced, or single) Height-weight relationship Underweight Slim, normal, stocky Overweight Obese Nonpregnant weight Mean 2 standard deviation (pounds)
Persons Mean
living with i standard
(
=
Last
Menstrual
*Separate
variance
tOne-tailed
test.
period.
df =
Degrees
/
No.
period
107.5
in two groups
(
%
92 28.6 51.1
grade
12.0 66.3
below
21.7
20.3 244
I
x2 = df= p ’
Y.YUY n nan n
J 6.01
119 41.9 56.0 2.1
230
/;:; 5.8
1;;
=
i.804
ip
<
0.01
=
4.676 2 0.05 (N.S.)
116 67.0 25.2 7.8
218
56.0 36.2 7.8
x2
df= P >
104 2.8 73.9 13.8 9.6
10.6 76.0 8.7 4.8
232 132.78 +27.8
112 125.85 222.5
176 4.2 + 1.7
91 4.8 -t 2.5
LMP
menstrual
Nonspecific %
182
infant after discharge deviation (persons)
last
x2 = df= P <
if
=
P
<
t t df
:
P
<
11.754 3 0.01 2.47 265.5* O.Olf
13::;: 0.05t
of freedom.
estimates.
was about 8 pounds among primiparas. According to a standard height-weight table, 3.8 times as many nonspecific mothers were underweight.8 The proportion was even higher among primiparas. Overweight and obese women were overrepresented in the specific last menstrual period group regardless of parity. Mothers in the nonspecific last menstrual period group were more frequently younger than 20 years at delivery if primiparous or older than 34 years if multiparous than the “exact” group mothers. Fewer of the “nonspecific last menstrual period” mothers had attended college. Multiparous women with nonspecific last menstrual periods were more likely not to have completed high school or to be more than 2 years behind their expected school grade if they were less than 19 years old. When categorized as single, married, and other, marital state was not different in the two last menstrual period
groups. “Other” included those who were widowed, separated, or divorced and comprised 7.8 per cent of both groups. However, when only married and single women were considered, the nonspecific last menstrual period mothers were almost one and one half times as often single (chi square = 4. 138; degrees of freedom = 1; p < .05). This general relationship was true regardless of parity, though it was stronger in primiparas. Following hospital discharge, “nonspecific last menstrual period” mothers, regardless of parity, and their newborn infants lived with more persons, though not in significantly more crowded circumstances. Significant differences were not found for the entire cohort in racial characteristics, number of previous pregnancies, number of children previously relinquished for adoption, social position of the father if mother was married or of the mother if she was
1076
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December Am. J. Obstet.
and Young
single ( Hollingshead’sT index), number of address changes in the year prior to the initial pediatric visit, number of social problems noted prenatally by the social workers, occurrence of initial prenatal hematocrit values less than 33 per cent, or exposure to possible teratogens, chiefly various types of psychedelic drugs. In the primiparous subsample, however, “nonspecific last menstrual period” women had a significantly lower social class, a significantly greater occurrence of hematocrit values less than 33 per cent, and a significantly greater number of social problems.
15, 1974 Gynecol.
Last menstrual period specificity as a risk indicator. Relatively little information was
indicator. Two British studies present data compatible with our hypothesis that women with nonspecific last menstrual periods experience more complications. Beazley and UnderhW found an increased obstetric complication rate in women with unknown expected dates of confinement. The incidence of fetal death was significantly higher in the group with unknown expected dates of confinement (chi square = 13.548; degrees of freedom = 1; p < 0.001) . The British Perinatal Study shows an increased infant mortality rate in pregnancies with “not known” gestational duration. l3 Information about the gestational duration in that study was obtained after the birth of the child. Last menstrual period specificity information is not reported. Because of this, the studies are not exactly comparable. “Not known” gestation is a variable that would appear to include almost all cases of nonspecific last menstrual periods but would not be limited to them. Our analysis of those data showed a significant association with “not known” gestational duration for low birth weight (chi square = 22.460; degrees of freedom = 1; p < O.OOl), intrapregnancy vaginal bleeding (chi square = 15.221; degrees of freedom = 1; p < O.OOl), and “toxemia” (chi square = 15.338; degrees of freedom = 1; p < 0.001) . The definition of toxemia in the British study is broad and includes women who may have had essential hypertension. Physicians’ awareness of problems when a woman reports a nonspecific last menstrual period has been largely confined to difficulties establishing the expected duration of pregnancy. This annoyance has been reduced by an increasing number of other means of determining the duration of gestation.14 That outcome problems are associated with patients reporting a nonspecific last menstrual period is demonstrated by the present data which show an increased rate of complications when a woman’s last menstrual period is nonspecific.
found in nonspecific
period
Comment
Incidence of nonspecific last menstrual periods. Approximately one third of the infants in the present study had mothers with nonspecific last menstrual periods. The percentage of nonspecific last menstrual periods (as defined in this study) reported by others varies widely, if it is reported at all. The information published on a large sample of pregnancies studied in the National Collaborative Project does not report the status of women’s last menstrual periods9 The highest reported incidence of nonspecific last menstrual periods found was in a series of 2,033 pregnancies studied to determine the per cent duration of gestation. lo Fifty-eight of the pregnancies were unsuitable for study because of nonspecific last menstrual period dates. Another study of 5, 686 single births with racial characteristics similar to those of our sample but with mothers whose average age was several years older had a 14.0 per cent incidence of nonspecific last menstrual periods.ll Beazley and Underhill’* studied 751 women, 165 of whom had unknown expected dates of confinement. They found that two thirds of the women with unknown expected dates of confinement (14.7 per cent of their total sample) had nonspecific last menstrual periods.
the literature with regard to a last menstrual period as a risk
Social disadvantage and last menstrual specificity. The findings in the present
Volume Number
120 8
cohort show that last menstrual period specificity is associated with some indicators of social disadvantage (see Table II). The social characteristics of the sample limit any generalization of these findings to women with poor social circumstances because the cohort was generally disadvantaged, as shown by measures of social position, etc., reported above. Therefore, the incidence of cases with nonspecific last menstrual period dates in other social circumstances cannot be discussed except by reference to other studies. The association of nonspecific last menstrual period dates with suboptimal social situations has been only indirectly explored by others. The births studied in the British Perinatal Study, which occurred across the full range of social classes, do show an association of “not known” gestational duration with social disadvantage.13 As discussed above, this variable, “not known” gestation, is similar to, but not identical with, nonspecific last menstrual period. In our analysis of the British Perinatal Study’s data, successively lower social class status was found to be significantly associated with an increasing proportion of “not known” gestations. This varied from 3.3 per cent in Social Class I to 10.2 per cent in Social Class V (chi square = 72.590; degrees of freedom = 4; p < 0.001). The incidence of “not known” gestations increased to 21.4 per cent in women who are delivered of infants when not married (chi square = 2,211; degrees of freedom = 1; p < 0.001). Twice as many women who became pregnant when less than 20 years old had “not known” gestations (chi square = 113; degrees of freedom = 1; p < 0.001). It could be postulated that disadvantaged social situations disorganize a woman’s life so that menstrual records are not kept accurately.
The origin of risk associated with last menstrual period specificity. When an explanation is sought for the association of patients with nonspecific last menstrual period dates and problems in reproduction, several possibilities occur. It is possible that vaginal bleeding, which is reported to be associated
Nonspecific
last
menstrual
period
1077
with poor reproductive outcome,15 might also cause a decrease in the ability to report a specific last menstrual period. In the present sample, vaginal bleeding was not significantly more common in nonspecific last menstrual period pregnancies and, therefore, could not be used as an explanation of the increased risk associated with a nonspecific last menstrual period. Irregular menstrual cycles might interfere with a woman’s ability to report the last menstrual period date since, in the present cohort, irregularity of menstrual cycles was reported more than twice as frequently by women who gave a nonspecific last menstrual period (chi square = 8.839; degrees of freedom = 1; p < 0.001). Of women in the “nonspecific” group, 18.7 percent reported irregular menses. Because of the possibility that some unexplained determinant of menstrual irregularity might adversely effect reproduction, the association of irregular menses with some reproductive outcomes was examined in the entire cohort. Infant birth weight, Apgar score at 1 minute, length of hospital stay of the infant after birth, number of previous stillbirths, number of previous prematurely born infants, and number of infants with congenital anomalies were all examined for association with irregular menses; associations were no s+ificant found. A woman’s last menstrual period can be nonspecific because she becomes pregnant prior to having a menstrual period following the birth of a child or because she becomes pregnant prior to menarche. Neither of these reasons occurred in this cohort. It is possible that the time interval from onset of the last menstrual period to the time of its reporting could influence the pregnant woman’s ability to report accurately. To investigate this possibility, the time interval was examined in the two groups. Interpretation of the data was complicated by problems with determining the duration of gestation to the time of the initial visit in the “nonspecific” group. The gestational duration for the “nonspecific”
1078
Wenner
and
December Am. J. Obstec.
Young
group was estimated by individual review of each record by one of the authors (W. H. W.) . These estimates considered all available information. Among the criteria were the available last menstrual period information, early pregnancy uterine size, date of hearing the fetal heart, infant birth weight, and recorded assessments of newborn maturity. Analysis of these data showed that the “nonspecific” group sought prenatal care 2 weeks further into pregnancy than the specific group. A 2 week addition to the average 22 weeks that elapsed prior to care being sought in the “specific date” group seemed a small increment to explain the difference in ability to report a specific last menstrual period. It also seemed that 2 additional weeks of medical care was insufficient to explain the difference in outcome. A woman’s seeking prenatal care later in pregnancy could be evidence of less optimal use of medical services or, more generally, poorer care of herself. In any case, interference with memory caused by increased time from the onset of the last menstrual period to the time of its report in the “nonspecific last menstrual period” group does not appear to clarify the reasons for a woman’s reporting a nonspecific last menstrual period. Another source of our finding that nonspecific last menstrual periods are associated with untoward reproductive events might be the association of women with nonspecific last menstrual period and disadvantaged social situations. The known association of disadvantaged social situations and poor reproductive outcome16 can be shown in the present cohort with its generally disadvan-
15, 1974 Gynecol.
taged characteristics. For example, there was a 9.8 per cent incidence of infants who were born weighing 2,500 grams or less. In contrast, the entire State of Washington, with its more varied social circumstances, recently had a 6.7 per cent incidence of such lowbirth weight infants. I7 Of special interest to this study is the finding that within the studied cohort the “nonspecific last menstrual period” group with its greater social disadvantages also had a higher incidence of infants born weighing 2,500 grams or less, namely, 14.1 per cent. The relationship to social disadvantage can perhaps be further elucidated by the findings when parity is considered. The primiparous subsample had evidence of having characteristics of generally greater risks: They were younger, were more often single, were of lower social class, had more numerous social problems, and were more frequently underweight and anemic. They also had poorer outcomes than multiparas in a majority of the variables. The outcomes were poorer still if they reported a nonspecific last menstrual period. Multiparous women with their better social circumstances showed the relationship between poor outcome and nonspecific last menstrual period less dramatically. Though the origin of the tie between nonspecific last menstrual period dates and poor outcome is explained here only at the level of an associative linkage, it is apparently the case that a nonspecifically reported date is an indicator which is able to select women within a socially disadvantaged cohort who will contribute disproportionately to the incidence of poor outcome.
REFERENCES
1. Nesbitt,
J.
4.
Alberman, E. D., and Goldstein, H.: Br. J. Prev. Sot. Med. 24: 129, 1970. Davie, R., Butler, N., and Goldstein, H.: The prediction of handicaps and an evaluation of the use of ‘at risk’ registers, in From Birth to Seven, London, 1972, Longmans, Green & Company.
5.
OBSTET.
2. 3.
R.
E. L.,
GYNECOL.
and
Aubry,
R. H.:
AM.
103: 972, 1969. 6. 7.
Aubry, R. H., and Pennington, H. C.: Clin. Obstet. Gynecol. 10: 3, 1973. Forfar, J. 0.: Dev. Med. Child Neurol. 10: 384, 1968. Feldstein, M. 8, and Butler, N. R.: Br. J. Prev. Sot. Med. 19: 128, 1965. Hollingshead, A. B.: Two factor index of social position, Copyright 1957 by the author (mimeograph).
Volume Number
8. 9.
10. 11. 12. 13.
120 8
Sargent, D. W.: Am. J. Clin. Nutr. 13: 318, 1963. Niswander, K. R., and Gordon, M.: The Women and Their Pregnancies, Philadelphia, 1972, W. B. Saunders Company. Hotelling, H., and Hotelling, F.: AM. J. OBSTET. GYNECOL. 23: 643, 1932. Anderson, N. A., Brown, E. W., and Lyon, R. A.: Am. J. Dis. Child. 65: 523, 1943. Beazley, J. M., and Underhill, R. A.: Nurs. Times 67: 1414, 1971. Butler, N. R., and Bonham, D. G.: Perinatal Mortality: The First Report of the 1958
Nonspecific
14. 15. 16. 17.
last menstrual
period
1079
Perinatal Mortality Survey, Edinburgh, 1963, E. & S. Livingstone, Ltd. Casaer, P., and Akiyama, Y.: Dev. Med. Child Neurol. 12: 697. 1970. Niswander, K. R.: Dkv. Med. Child Neural. 12: 398, 1970. Osofsky, H. J., and Kendall, N.: Clin. Obstet. Gynecol. 16: 103, 1973. United States Department of Health, Education, and Welfare, Public Health Service: Vital Statistics of the United States, 1968, Natality, Washington, D. C., 1970, vol. 1, United States Government Printing Office.
indication
of
WALDEMAR E.
H.
BERT
Seattle,
YOUNG,
poor
reproductive
WENNER,
outcome
M.D.
B.A.
Washington
Socially disadvantaged women whose medical records showed they reported nonspecific last menstrual period dates at the first prenatal visit had a disproportionately high incidence of complications in reproduction. The complications included an increased likelihood of delivery by cesarean section and lighter, more immature infants. Nonspecific last menstrual periods were also associated with indicators of increased risk available early in pregnancy. The increased number of complications among disadvantaged women with nonspecific last menstrual period dates was not explained by prenatal vaginal bleeding or irregular menstrual periods. A possible explanation for the association appeared to be the social circumstances. Mothers who reported nonspecific last menstrual period dates tended to be mothers with more disadvantaged social circumstances. These circumstances have been found to be associated with poor reproductive outcome.
T H E A B I L I T Y to anticipate problems is crucial in providing quality medical care to large numbers of pregnant women and their offspring. Improvement of this ability through the use of systematic risk assessment procedures has been previously explored.ll 2 IdentiFrom the Department the Child Development Retardation Center, Washington.
of Pediatrics
fication of “at-risk” patients can provide a basis for the allocation of appropriate health and social services and, concomitantly, can decrease to appropriate levels the intensity of surveillance for problems in the general population.3p 4 Risk identification has had varying degrees of sophistication, ranging from simple listing of individual indicators of poor outcome to compilations that weigh a multitude of indicators relative to their combined impact on outcome. 5l 6 Two means of improving the identification of “at-risk” patients are: ( 1) demonstration of previously unrecognized or undervalued factors or procedures indicating increased risk, and (2) elucidation of the interrelationships of risk factors. In an effort to improve the identification of “at-risk” infants, medical and social information was examined in a cohort of 357 infants. This information had been considered in clinical decisions about the inclusion of perinates in a high-risk infant followup program. Among the factors considered was maternal uncertainty about the specific date of the last menstrual period. Initially, this factor was included because of interest
and
and Mental University of
Supported by a grant from the Washinaton Association for Retarded Children Trust Fund; by Project No. 913, Maternal and Child Health Service, Health Services and Mental Health Administration, Department of Health, Education, and Welfare; by Grant No. HO02274 from the National Institute of Child Health and Human Development, National Institutes of Health, Department of Health, Education, and Welfare; and by Contract No. N.I.H. 71-4174, Division of Nursing, National Institutes of Health, Department of Health, Education, and Welfare. Received 1974. Revised Accepted
for publication April May
27,
January
15,
1974.
8, 1974.
Reprint requests: Dr. Waldemar Wenner, SC-74, University of Washington, Seattle, Washington
H. 98195. 1071
1072
Wenner
and Young
in information pertinent to the determination of gestational age and prematurity, themselves factors of central interest. However, a strong tendency was found for mothers who reported nonspecific last menstrual period dates to have given birth to infants who were considered “high risk.” Of infants on whom a “risk” decision was made, 66 per cent whose mothers reported nonspecific last menstrual periods were enrolled in the high risk follow-up program; only 38 per cent of infants born to mothers with specific last menstrual period dates were enrolled (chi square = 22.696; degrees of freedom = 1; p < 0.001). This was unexpected because last menstrual period date “specificity” was not among the decision criteria which included a variety of medical and psychosocial factors. This association of last menstrual period specificity with clinical decisions concerning probable risk suggested that last menstrual period specificity itself deserved examination as an indicator of increased risk. Questions to be answered by this inquiry were: ( 1) Is lack of last menstrual period specificity associated with increased risk of poor maternal and fetal outcome? (2) What are the relationships of last menstrual period specificity to risk indicators which can be obtained early in pregnancy? Method
Subjects. Infants whose mothers receive prenatal care at University Hospital under the auspices of the Seattle-King County Health Department’s Maternal and Infant Care Program are referred for pediatric care to the Child Development and Mental Retardation Center unless they are relinquished for adoption or die prior to referral. To be eligible for this program, at the time of enrollment the mothers must reside in certain areas of Seattle with high infant morbidity and mortality rates. Between July 1, 1969, and June 30, 1970, 357 infants were referred. The mothers tended to be young (median age, 19.86 years, mean age, 21.14 years), urban, of low social position (66 per cent of heads of household in Hollingshead’s7 Class
Am.
December J. Obstet.
15, 1974 Gynecol.
V and an additional 24 per cent in Class IV), often primiparous (57 per cent), and single (29 per cent). Among the multiparous women, 41 per cent were having their second pregnancy; 24 per cent, their third; and 15 per cent their fourth. The racial and cultural backgrounds were mixed (54 per cent white, 37 per cent black, 9 per cent Native American, Eskimo, Chicano, and Oriental). Mothers were placed in the “specific” last menstrual period group (No. = 235) if their records showed that a date, specific to the day, for the start of the last menstrual period was reported at the initial visit to the obstetrician. Mothers who did not report a specific date were placed in the “nonspecific” last menstrual period group (No. = 120) . Nonspecific last menstrual period date entries included early-, middle-, or late-month entries, specific only to the week, no entry when the rest of the obstetric history was present, and notation of “unknown” or “questionable.” Data collection. The information was tabulated from maternal and infant medical records and from a demographic record completed by the mother at the infant’s first pediatric visit. Professional staff compiling the records included nutritionists, physicians, public health nurses, and social workers. Data were taken from the charts by 4 trained coders whose interobserver reliability was maintained at the 95 per cent level of agreement for all variables. They used a coding manual developed for this population. It defined each of the variables in mutually exclusive and exhaustive categories, rankings, or intervals. Inconsistencies in the record were treated as missing information. The accuracy of the information found in the medical record could, of course, not be controlled for. It was assumed to be acceptable for use in this exploratory study. A separate analysis of the relative amounts of missing information in each of the two last menstrual period groups failed to show that either group was more prone to have missing information. Some variables were combined and some categorizations were collapsed for analysis.
Volume Number
120 8
Nonspecific
Table I. Maternal
and fetal outcome
proteinuria Specific LMP
Prenatal
Nonspecific Delivery
>
compared
Nonspecific
5
Nonspecific
10.0
x2
117
“1.4
df= P -=C
7.481 1 0.01
226
1.8
119
a.4
x2 x df= i P -=C
9.180 1 0.005
“34
15.4
x2 z.z df=
120
29.2
8.557 1 0.005
a$neic
231
0.9
x’
df= P -C
4.467 1 0.05
I
i
=
section
6
LMP
or more
in two groups
230
Specific LMP One
1073
trace
LMP
Apgar
period
%
Specific LMP I Minute
menstrual
No.
LMP
by cesarean
last
i
P
.<
episodes
Specific LMP
Ez
Nonspecific LMP muscle tone abnormality Specific LMP
119
5.0
i
230
1.7
Nonspecific
118
7.6
x2 zzz df= i P <
5.970 1 0.025
Specific LMP
232
10.3
Nonspecific
119
20.2
x2 = df= i P <
5.624 1 0.02.5
233
2.1
119
9.2
x2 = df= i P <
7.583 1 0.01
Specific LMP
232
3,294.27* rt 539.6
Nonspecific
115
3,111.12* + 594.7
Infant
Infant
LMP
hospital
Gavage-fed
stay
>
4 days
LMP infant
Specific LMP Nonspecific Infant
birth
LMP weight
(singletons)
LMP
LMP = Last menstrual period. *Mean
I ! standard
tOne-tailed
deviation
in
df
=
Degrees
t = 2.08 df = 345 0.002t P = .-
of freedom.
grams.
test.
Results
Association of last menstrual period specificity with poor reproductive outcome. To determine whether mothers who reported nonspecific last menstrual period dates were at increased risk of poor maternal and fetal outcome, 23 variables relating to complications of the pregnancy, delivery, or hospital course of the newborn infant were examined. Some possible complications such as neonatal convulsions had veri low or absent occurrence rates in this cohort and, therefore, were not examined. The following significant associations were found (Table I) : Women in the nonspecific group were almost 5 times as likely to be
delivered by cesarean section. The proportion of cesarean sections occasioned by a previous cesarean section was approximately equal in the two groups, 25 per cent in the “exact” group and 30 per cent in the “nonspecific” group. The reasons for primary cesarean sections in both groups included: relative cephalopelvic disproportion (4 cases), failure of progression of labor (3 cases), cord prolapse (1 case), and fetal distress (1 cltsej. The mean birth weight of singleton infants whose mothers reported a nonspecific last menstrual period was 3,111 grams, 183 grams less than that of infants born to women reporting a specific last menstrual period. Accompanying the birth weight dif-
1074
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and
Young Am.
ference were other suggestions of an increased incidence of immature infants: Gavage feeding and apneic episodes were approximately 5 times greater; abnormalities of muscle tone (either hyper- or hypo-tonus was noted at least twice while the infant was in the newborn nursery) were about 4vz times more frequent; twice as many of the infants of mothers in the nonspecific group stayed in the hospital longer than 4 days; the mean duration of hospitalization was 5.2 days, almost 2 days longer than infants born to mothers with exact last menstrual periods. Determination of the relation of size to gestational age is difficult to interpret because of questions about gestational age in the nonspecific last menstrual period group. This relationship is not reported for that reason. Proteinuria greater than trace was twice as frequent in the nonspecific last menstrual period group of pregnancies. Infants of women with nonspecific last menstrual periods had 1 minute Apgar scores of 6 or less almost twice as often. For both primiparous and multiparous women, the proportion with nonspecific last menstrual period dates approximated one third. The pregnancy outcome variables found to be significantly associated with last menstrual period specificity status and enumerated above almost all showed a greater occurrence of poor outcome if a woman reported a nonspecific last menstrual period, whether the mother was having the first or a subsequent pregnancy. The exception was the variable “duration of hospital stay of the infant after birth”; the infants of multiparas with specific last menstrual periods stayed a nonsignificant one tenth of a day longer than those of nonspecific last menstrual period multiparas. Only associations within the primiparous subsample, and not all of these, maintained statistical significance when the total cohort was subdivided according to parity. The remaining 15 variables included hyperemesis gravidarum, prenatal vaginal bleeding, prenatal urinary tract infection, maternal hypertension, use of magnesium
December J. Obstet.
15, 1974 Gynecol.
sulfate during labor and delivery, use of indicated forceps, duration of the second stage of labor, abnormalities of the fetal heart rate during labor or delivery, meconium staining of the amniotic fluid, 5 minute Apgar scores below 6, infant temperatures below 36’ C. following a recording above that level, number of instances of infant jitteriness, hours elapsing after birth before infants who were not gavage fed were reported to have taken two successive feedings well, cyanosis with feedings, and congenital anomalies. Among these variables where significant associations were not found in the entire sample, the nonspecific last menstrual period group contained a greater proportion of individuals having complications in 10. Thus, in 78 per cent of all the variables examined in the entire cohort, there was a greater proportion of individuals with poor outcome in the nonspecific last menstrual period group. This was also true in the multiparous subsample. This proportion increased to 83 per cent among the primiparous subsample. However, first-time mothers showed a significantly increased incidence of both abnormalities of the fetal heart during labor and the use of indicated forceps if they reported specific last menstrual periods. These two were the only significant associations among the 69 examined that were contrary to the hypothesis that women who report nonspecific last menstrual period dates tend to have an increased incidence of poor reproductive outcome.
Relationship of last menstrual period specificity to known risk indicators. The relationships of last menstrual period specificity to other risk characteristics available early in pregnancy were determined by examining 15 variables relating to maternal prepregnancy medical status, to demographic descriptors of the mother, and to social conditions that might influence the mother and her offspring. The following significant associations were found (Table II) : The mothers’ reports of their nonpregnant weight showed the nonspecific last menstrual period group to be 7 pounds lighter. The difference
Volume Number
120 8
Nonspecific
Table II. Medical,
demographic,
and social risk indicators
compared
Specific Indicator
No.
Maternal education Beyond high school Completed high school or age-appropriate Did not complete high school or grade age level Maternal age Less than 20 years 20 to 34 years Greater than 34 years Marital status at delivery Married Single Other (widowed, divorced, or single) Height-weight relationship Underweight Slim, normal, stocky Overweight Obese Nonpregnant weight Mean 2 standard deviation (pounds)
Persons Mean
living with i standard
(
=
Last
Menstrual
*Separate
variance
tOne-tailed
test.
period.
df =
Degrees
/
No.
period
107.5
in two groups
(
%
92 28.6 51.1
grade
12.0 66.3
below
21.7
20.3 244
I
x2 = df= p ’
Y.YUY n nan n
J 6.01
119 41.9 56.0 2.1
230
/;:; 5.8
1;;
=
i.804
ip
<
0.01
=
4.676 2 0.05 (N.S.)
116 67.0 25.2 7.8
218
56.0 36.2 7.8
x2
df= P >
104 2.8 73.9 13.8 9.6
10.6 76.0 8.7 4.8
232 132.78 +27.8
112 125.85 222.5
176 4.2 + 1.7
91 4.8 -t 2.5
LMP
menstrual
Nonspecific %
182
infant after discharge deviation (persons)
last
x2 = df= P <
if
=
P
<
t t df
:
P
<
11.754 3 0.01 2.47 265.5* O.Olf
13::;: 0.05t
of freedom.
estimates.
was about 8 pounds among primiparas. According to a standard height-weight table, 3.8 times as many nonspecific mothers were underweight.8 The proportion was even higher among primiparas. Overweight and obese women were overrepresented in the specific last menstrual period group regardless of parity. Mothers in the nonspecific last menstrual period group were more frequently younger than 20 years at delivery if primiparous or older than 34 years if multiparous than the “exact” group mothers. Fewer of the “nonspecific last menstrual period” mothers had attended college. Multiparous women with nonspecific last menstrual periods were more likely not to have completed high school or to be more than 2 years behind their expected school grade if they were less than 19 years old. When categorized as single, married, and other, marital state was not different in the two last menstrual period
groups. “Other” included those who were widowed, separated, or divorced and comprised 7.8 per cent of both groups. However, when only married and single women were considered, the nonspecific last menstrual period mothers were almost one and one half times as often single (chi square = 4. 138; degrees of freedom = 1; p < .05). This general relationship was true regardless of parity, though it was stronger in primiparas. Following hospital discharge, “nonspecific last menstrual period” mothers, regardless of parity, and their newborn infants lived with more persons, though not in significantly more crowded circumstances. Significant differences were not found for the entire cohort in racial characteristics, number of previous pregnancies, number of children previously relinquished for adoption, social position of the father if mother was married or of the mother if she was
1076
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December Am. J. Obstet.
and Young
single ( Hollingshead’sT index), number of address changes in the year prior to the initial pediatric visit, number of social problems noted prenatally by the social workers, occurrence of initial prenatal hematocrit values less than 33 per cent, or exposure to possible teratogens, chiefly various types of psychedelic drugs. In the primiparous subsample, however, “nonspecific last menstrual period” women had a significantly lower social class, a significantly greater occurrence of hematocrit values less than 33 per cent, and a significantly greater number of social problems.
15, 1974 Gynecol.
Last menstrual period specificity as a risk indicator. Relatively little information was
indicator. Two British studies present data compatible with our hypothesis that women with nonspecific last menstrual periods experience more complications. Beazley and UnderhW found an increased obstetric complication rate in women with unknown expected dates of confinement. The incidence of fetal death was significantly higher in the group with unknown expected dates of confinement (chi square = 13.548; degrees of freedom = 1; p < 0.001) . The British Perinatal Study shows an increased infant mortality rate in pregnancies with “not known” gestational duration. l3 Information about the gestational duration in that study was obtained after the birth of the child. Last menstrual period specificity information is not reported. Because of this, the studies are not exactly comparable. “Not known” gestation is a variable that would appear to include almost all cases of nonspecific last menstrual periods but would not be limited to them. Our analysis of those data showed a significant association with “not known” gestational duration for low birth weight (chi square = 22.460; degrees of freedom = 1; p < O.OOl), intrapregnancy vaginal bleeding (chi square = 15.221; degrees of freedom = 1; p < O.OOl), and “toxemia” (chi square = 15.338; degrees of freedom = 1; p < 0.001) . The definition of toxemia in the British study is broad and includes women who may have had essential hypertension. Physicians’ awareness of problems when a woman reports a nonspecific last menstrual period has been largely confined to difficulties establishing the expected duration of pregnancy. This annoyance has been reduced by an increasing number of other means of determining the duration of gestation.14 That outcome problems are associated with patients reporting a nonspecific last menstrual period is demonstrated by the present data which show an increased rate of complications when a woman’s last menstrual period is nonspecific.
found in nonspecific
period
Comment
Incidence of nonspecific last menstrual periods. Approximately one third of the infants in the present study had mothers with nonspecific last menstrual periods. The percentage of nonspecific last menstrual periods (as defined in this study) reported by others varies widely, if it is reported at all. The information published on a large sample of pregnancies studied in the National Collaborative Project does not report the status of women’s last menstrual periods9 The highest reported incidence of nonspecific last menstrual periods found was in a series of 2,033 pregnancies studied to determine the per cent duration of gestation. lo Fifty-eight of the pregnancies were unsuitable for study because of nonspecific last menstrual period dates. Another study of 5, 686 single births with racial characteristics similar to those of our sample but with mothers whose average age was several years older had a 14.0 per cent incidence of nonspecific last menstrual periods.ll Beazley and Underhill’* studied 751 women, 165 of whom had unknown expected dates of confinement. They found that two thirds of the women with unknown expected dates of confinement (14.7 per cent of their total sample) had nonspecific last menstrual periods.
the literature with regard to a last menstrual period as a risk
Social disadvantage and last menstrual specificity. The findings in the present
Volume Number
120 8
cohort show that last menstrual period specificity is associated with some indicators of social disadvantage (see Table II). The social characteristics of the sample limit any generalization of these findings to women with poor social circumstances because the cohort was generally disadvantaged, as shown by measures of social position, etc., reported above. Therefore, the incidence of cases with nonspecific last menstrual period dates in other social circumstances cannot be discussed except by reference to other studies. The association of nonspecific last menstrual period dates with suboptimal social situations has been only indirectly explored by others. The births studied in the British Perinatal Study, which occurred across the full range of social classes, do show an association of “not known” gestational duration with social disadvantage.13 As discussed above, this variable, “not known” gestation, is similar to, but not identical with, nonspecific last menstrual period. In our analysis of the British Perinatal Study’s data, successively lower social class status was found to be significantly associated with an increasing proportion of “not known” gestations. This varied from 3.3 per cent in Social Class I to 10.2 per cent in Social Class V (chi square = 72.590; degrees of freedom = 4; p < 0.001). The incidence of “not known” gestations increased to 21.4 per cent in women who are delivered of infants when not married (chi square = 2,211; degrees of freedom = 1; p < 0.001). Twice as many women who became pregnant when less than 20 years old had “not known” gestations (chi square = 113; degrees of freedom = 1; p < 0.001). It could be postulated that disadvantaged social situations disorganize a woman’s life so that menstrual records are not kept accurately.
The origin of risk associated with last menstrual period specificity. When an explanation is sought for the association of patients with nonspecific last menstrual period dates and problems in reproduction, several possibilities occur. It is possible that vaginal bleeding, which is reported to be associated
Nonspecific
last
menstrual
period
1077
with poor reproductive outcome,15 might also cause a decrease in the ability to report a specific last menstrual period. In the present sample, vaginal bleeding was not significantly more common in nonspecific last menstrual period pregnancies and, therefore, could not be used as an explanation of the increased risk associated with a nonspecific last menstrual period. Irregular menstrual cycles might interfere with a woman’s ability to report the last menstrual period date since, in the present cohort, irregularity of menstrual cycles was reported more than twice as frequently by women who gave a nonspecific last menstrual period (chi square = 8.839; degrees of freedom = 1; p < 0.001). Of women in the “nonspecific” group, 18.7 percent reported irregular menses. Because of the possibility that some unexplained determinant of menstrual irregularity might adversely effect reproduction, the association of irregular menses with some reproductive outcomes was examined in the entire cohort. Infant birth weight, Apgar score at 1 minute, length of hospital stay of the infant after birth, number of previous stillbirths, number of previous prematurely born infants, and number of infants with congenital anomalies were all examined for association with irregular menses; associations were no s+ificant found. A woman’s last menstrual period can be nonspecific because she becomes pregnant prior to having a menstrual period following the birth of a child or because she becomes pregnant prior to menarche. Neither of these reasons occurred in this cohort. It is possible that the time interval from onset of the last menstrual period to the time of its reporting could influence the pregnant woman’s ability to report accurately. To investigate this possibility, the time interval was examined in the two groups. Interpretation of the data was complicated by problems with determining the duration of gestation to the time of the initial visit in the “nonspecific” group. The gestational duration for the “nonspecific”
1078
Wenner
and
December Am. J. Obstec.
Young
group was estimated by individual review of each record by one of the authors (W. H. W.) . These estimates considered all available information. Among the criteria were the available last menstrual period information, early pregnancy uterine size, date of hearing the fetal heart, infant birth weight, and recorded assessments of newborn maturity. Analysis of these data showed that the “nonspecific” group sought prenatal care 2 weeks further into pregnancy than the specific group. A 2 week addition to the average 22 weeks that elapsed prior to care being sought in the “specific date” group seemed a small increment to explain the difference in ability to report a specific last menstrual period. It also seemed that 2 additional weeks of medical care was insufficient to explain the difference in outcome. A woman’s seeking prenatal care later in pregnancy could be evidence of less optimal use of medical services or, more generally, poorer care of herself. In any case, interference with memory caused by increased time from the onset of the last menstrual period to the time of its report in the “nonspecific last menstrual period” group does not appear to clarify the reasons for a woman’s reporting a nonspecific last menstrual period. Another source of our finding that nonspecific last menstrual periods are associated with untoward reproductive events might be the association of women with nonspecific last menstrual period and disadvantaged social situations. The known association of disadvantaged social situations and poor reproductive outcome16 can be shown in the present cohort with its generally disadvan-
15, 1974 Gynecol.
taged characteristics. For example, there was a 9.8 per cent incidence of infants who were born weighing 2,500 grams or less. In contrast, the entire State of Washington, with its more varied social circumstances, recently had a 6.7 per cent incidence of such lowbirth weight infants. I7 Of special interest to this study is the finding that within the studied cohort the “nonspecific last menstrual period” group with its greater social disadvantages also had a higher incidence of infants born weighing 2,500 grams or less, namely, 14.1 per cent. The relationship to social disadvantage can perhaps be further elucidated by the findings when parity is considered. The primiparous subsample had evidence of having characteristics of generally greater risks: They were younger, were more often single, were of lower social class, had more numerous social problems, and were more frequently underweight and anemic. They also had poorer outcomes than multiparas in a majority of the variables. The outcomes were poorer still if they reported a nonspecific last menstrual period. Multiparous women with their better social circumstances showed the relationship between poor outcome and nonspecific last menstrual period less dramatically. Though the origin of the tie between nonspecific last menstrual period dates and poor outcome is explained here only at the level of an associative linkage, it is apparently the case that a nonspecifically reported date is an indicator which is able to select women within a socially disadvantaged cohort who will contribute disproportionately to the incidence of poor outcome.
REFERENCES
1. Nesbitt,
J.
4.
Alberman, E. D., and Goldstein, H.: Br. J. Prev. Sot. Med. 24: 129, 1970. Davie, R., Butler, N., and Goldstein, H.: The prediction of handicaps and an evaluation of the use of ‘at risk’ registers, in From Birth to Seven, London, 1972, Longmans, Green & Company.
5.
OBSTET.
2. 3.
R.
E. L.,
GYNECOL.
and
Aubry,
R. H.:
AM.
103: 972, 1969. 6. 7.
Aubry, R. H., and Pennington, H. C.: Clin. Obstet. Gynecol. 10: 3, 1973. Forfar, J. 0.: Dev. Med. Child Neurol. 10: 384, 1968. Feldstein, M. 8, and Butler, N. R.: Br. J. Prev. Sot. Med. 19: 128, 1965. Hollingshead, A. B.: Two factor index of social position, Copyright 1957 by the author (mimeograph).
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8. 9.
10. 11. 12. 13.
120 8
Sargent, D. W.: Am. J. Clin. Nutr. 13: 318, 1963. Niswander, K. R., and Gordon, M.: The Women and Their Pregnancies, Philadelphia, 1972, W. B. Saunders Company. Hotelling, H., and Hotelling, F.: AM. J. OBSTET. GYNECOL. 23: 643, 1932. Anderson, N. A., Brown, E. W., and Lyon, R. A.: Am. J. Dis. Child. 65: 523, 1943. Beazley, J. M., and Underhill, R. A.: Nurs. Times 67: 1414, 1971. Butler, N. R., and Bonham, D. G.: Perinatal Mortality: The First Report of the 1958
Nonspecific
14. 15. 16. 17.
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period
1079
Perinatal Mortality Survey, Edinburgh, 1963, E. & S. Livingstone, Ltd. Casaer, P., and Akiyama, Y.: Dev. Med. Child Neurol. 12: 697. 1970. Niswander, K. R.: Dkv. Med. Child Neural. 12: 398, 1970. Osofsky, H. J., and Kendall, N.: Clin. Obstet. Gynecol. 16: 103, 1973. United States Department of Health, Education, and Welfare, Public Health Service: Vital Statistics of the United States, 1968, Natality, Washington, D. C., 1970, vol. 1, United States Government Printing Office.