Cesarean section and subsequent fertility: results from the 1982 National Survey of Family Growth

Vol. 43. No.4, April 1985 Printed in U.SA.

FERTILITY AND STERILITY Copyright © 1985 The American Fertility Society

Cesarean section and subsequent fertility: results from the 1982 National Survey of Family Growth

Elina Hemminki, M.D.* Barry I. Graubard, M.A. t Howard J. Hoffman, M.A. t William D. Mosher, Ph.D.t Karen Fetterly, B.S. t National Institute of Child Health and Human Development, Bethesda, Maryland, University of Tampere, Tampere, Finland, and National Center for Health Statistics, Hyattsville, Maryland

The purpose of this article was to examine the question of fertility after a cesarean section. The study design is that of a retrospective cohort study with matched pairs, using the cross-sectional interview data of the 1982 National Survey of Family Growth. The subsequent fertility of 406 women who had had their first delivery by cesarean section is compared with that of 406 matched control women. Using any of several measures, women who had had a cesarean section had lower fertility. The difference in fertility seemed to result largely from difficulties in having children after a cesarean section, rather than lessened desire for children. Sterilizations were more frequent and performed earlier among women who had had a cesarean section than among the control women. Fertil Steril43:520, 1985

About one in five births in the United States is now delivered by cesarean section. 1 Before the 1960s, when cesarean section was rare and also more dangerous, lower fertility was assumed to follow cesarean section and was recognized then as an important issue. 2 Recently, two studies, one from upstate New York 3 and the other from Sweden,4 showed that women who had had a cesarean section in their first delivery had 11% to 13% fewer second children in the next 5 years, when Received July 27, 1984; revised and accepted December 4, 1984. . *Reprint requests: Elina Hemminki, M.D., Department of Public Health, University of Tampere, PL 607, 3310 Tampere 10, Finland. tEpidemiology and Biometry Research Program, National Institute of Child Health and Human Development. :j:Family Growth Survey Branch, National Center for Health Statistics. 520

compared with a matched group of women who had had a vaginal delivery. Because both of these studies were based on existing registries, no information about the reasons for the smaller number of children was available. The purpose of this article was to examine some of the effects of this increasingly common procedure on the future fertility of the women affected. We investigated whether the finding oflower fertility among women with cesarean section prevails for a sample of women from a national fertility survey of the United States population, and, if so, whether it is due to personal preference or reduced fecundity.*

Hemminki et al. Cesarean section and subsequent fertility

*In this article we follow the demographic usage: "fertility" is the actual number of births women have, whereas "fecundity" is the physical ability to bear children.

Fertility and Sterility

MATERIALS AND METHODS

The data are from cycle III of the National Survey of Family Growth (NSFG), conducted by the National Center for Health Statistics. The NSFG, which was conducted in 1973, 1976, and 1982, is a multipurpose survey of women 15 to 44 years of age, designed to produce national estimates of trends and group differences in factors related to childbearing. These include marriage, divorce, and remarriage, the timing of first intercourse, contraceptive practice, infertility, surgical sterilization, breast-feeding, and related aspects of reproductive and infant health. The survey is based on personal interviews with a nationwide area probability sample of women 15 to 44 years of age in the noninstitutional population of the United States, excluding Alaska and Hawaii. Women were interviewed in their homes by trained female interviewers using a standard questionnaire. The questionnaire included a complete pregnancy history for each respondent, including live births, pregnancy losses, and abortions, past and current contraceptive practice, the wantedness of existing children and intended future births, her physical ability to have children, use of family planning and infertility services, and a wide range of socioeconomic characteristics. A report of selected findings from cycle III was published elsewhere. 5 The findings of cycles I and II on contraception, infertility, breast-feeding, and other topics were summarized by Mosher. 6 In cycle III, 7969 women were interviewed between August 1982 and February 1983, including 3201 black, 4577 Caucasian, and 191 women of other races. Black women and teenage women were oversampled. The cross-sectional data of this survey were used to create a retrospective cohort study. Women who had had no livebirths (n = 3356) were excluded. Also, women who had had two or more abortions (either spontaneous or induced) before their first live birth, whose first child was born dead, or whose first birth was a multiple delivery (n = 193) were excluded. After these exclusions, there were 4420 women, of whom 426 had had their first live birth (hereafter, first .birth or first child) by cesarean section. The information regarding the mode of delivery was lacking for nine women, and they were excluded. Women whose first child died within the first year of life or whose infant weighed less than 1500 gm at birth (11 women in the cesarean section group and 93 Vol. 43, No.4, April 1985

among the rest) or was given up for adoption (2 and 13 women, respectively) were also excluded, leaving 4292 women. Of these women, 413 had had their first child by cesarean section (C-sectioned women), and another 3879 women had had a vaginal delivery. For each C-sectioned woman a control subject was selected from women who had had vaginal deliveries by matching for the date of the first birth (± 6 months), the mother's age at interview (± 1 year), the mother's race (black, Caucasian, other), and marital status at the time of the first birth (married, unmarried). The first two factors combined also control for mother's age at the time of the first birth. The woman was defined to be married ifher first marriage had occurred prior to the first birth. Based upon these matching criteria, a control woman was found for 390 C-sectioned women. An additional 16 pairs were found by selecting a Caucasian control subject for women of "other" race (6 pairs) and by relaxing the age of the woman to ± 2 years (10 pairs). The remaining seven women were excluded from the study, leaving a total of 406 matched pairs. Because the objective of this article was to determine whether cesarean section affects future fertility and not to make national estimates, the sampling weights were not used. The statistical significance of the differences in proportions of binary variables and of the means of continuous variables were tested with McNemar's test and the paired t-test, respectively, in order to take the matched design into account. However, the matched pairs were not retained for testing statistical differences for proportions based only upon women who had a second child, because of the reduced sample size due to the loss of pairs when one or the other mother did not have a second child. The Pearson chi-square test was used to test for significant differences in categorical variables with more than two levels. The Kaplan-Meier procedure, a life-table method, was used to estimate the distributions of the time between the first and second live births, and the time between the first live birth and sterilization between the C-sectioned and control women. 7 Women who did not have a second live birth or were not sterilized by the date of the interview (censored observations) were included in the analysis. Median lengths of time were calculated from these estimated time distributions. MantelCox test statistics were used to test for differences between the C-sectioned and control women with

Hemminki et al. Cesarean section and subsequent fertility

521

respect to the time distributions. 7 In order to ad~ just for potential confounding background variables, multiple logistic analysis and multiple linear regression analysis were performed to estimate odds ratios for binary outcome variables and mean differences for continuous outcome variables, respectively. In order to examine the differing effects by race and to help draw generalizations to other types of populations, most results are presented by race. The results were studied also by the time period of the first birth because of the dramatic changes in the patterns of cesarean section over the last 20 years. The time periods were defined as before 1968, 1968 to 1972, 1973 to 1977, and 1978 to 1983.

RESULTS C-sectioned and control women were very similar with regard to most background variables, as shown in Table 1. The first four characteristics listed in Table 1 are the matching variables. The two groups were very similar in these characteristics, as expected. About 6% of the women were less than 20 years of age and 20% were 35 years or over at the time of the interview. The oldest child was born in 1957 and the youngest in 1982; however, most of the children were born in the latter half of the 1970s or in the early 1980s. The C-sectioned and control women were also very similar with regard to other background variables. In addition to the items described in Table 1, the two groups were compared in terms of the mean number of marriages (1.1), distribution by four geographic areas within the United States, proportion of Protestants (73%)~ age at the time of the first birth (mean, 21.9 years), and the sex of the first child (52% of the C-sectioned and 55% of the control women had a boy). Th.ere was no difference in the "wantedness" of the first pregnancy (whether the pregnancy occurred later or earlier than wanted, or on time, or was unwanted). As expected, the first child of the C-sectioned women had congenital health problems more often (13.2% versus 6.7%), and. the child stayed longer in the hospital' (even though the hospital stay of women with cesarean sections apparently was longer, 7.9% of their children stayed longer than the mother,. compared with 6.7% in the control group). Also, children of the C-sectioned women were less frequently breastfed (34% versus 40%). The information on congen522.

ital health problems and hospital stay was available only for children born in January 1979 or later. In the control group, there were seven women (1.7%) who had a cesarean section in their later pregnancies. There was no difference in the proportion of first children living in the mother's households at the time of the interview (94% for the C-sectioned women and 95% for the control women). The mean number of subsequent pregnancies and live-born children after the first child was smaller (about 11%) among the C-sectioned women as compared with the control women, although the differences were not statistically significant (Table 2). The proportion of women who had had no additional pregnancies or live births until the" interview was similar among C-sectioned and control women, but 13% of the C-sectioned women had had two or more additional children, compared with 17% of the control women. Among women who had had a second pregnancy, the mean time interval between the first child and the next live birth was 3.7 years among C-sectioned women and 3.2 years among the control women (P < 0.05). However, when all women

Hemminki et aI. Cesarean section andsuosequent fertility

Table 1. Descriptwn of the C-Sectioned and Control Women by Background Variablesa C-sectioned (n

Matched variables Mean age of women (yr) Year of first birth < 1968 (%) 1968-72 (%) 1973-77 (%) 1978-83(%) Black (%) Married at time of first birth (%) Other variables Married (%) Mean years of education Less than 12 years of education (%) Catholic (%) Hispanic (%) Living in a central city (%) One spontaneous abortion prior to first child (%) One induced abortion prior to first child (%) First child Mean birthweight (gm) First prenatal visit to private doctor or group practice b (%)

= 406)

Control (n

= 406)

28.5

28.6

8 15 30 47 45 71

8 15 30 47 45 71

68 12.5 25

70 12.8 19

22 9 44 8

17 6 40 9

6

6

3376 66

3274c 65

aAt the time of the interview, unless specified otherwise. bOnly births occurring January 1979. or later. cp.< 0.01.

Fertility and Sterility

Table 2. Actual Pregnancies After the First Child (A) and Births Intended to Occur (B), by Race All women C-sectioned Control (n

A: Actual Mean no. of pregnancies Mean no. of live births Median interval to second live-born (yrs)b No pregnancies (%) No live births (%) One or more spontaneous abortions (%) One or more induced abortions (%) B: Intended Mean no. of intended births Mean total no. of births

= 406)

(n

0.99 0.69 3.7

= 406)

Black C-sectioned Control (n

1.11 0.78 3.8

= 182)

0.98 4.1

38 47 11

36 46

12

16 0.72c 2.52d

= 182)

(n

1.11 0.78 4.4

0~71

37 47 12

0.59 2.28

(n

Caucasiana C-sectioned Control = 224)

(n

0.99 0.68 3.7

= 224)

1.11 0.78 3.2

11

41 49 9

38 47 13

36 46 13

12

19

13

13

0.77 c 2.58e

0.55 2.25

0.62 2.31

0.67 2.46

aIncludes also women of races other than Caucasian and black. bAll women are included; those not having a second live birth are included as censored observations. cp < 0.05. dp < 0.001. ep < 0.01.

were included, where women who had not had a second pregnancy were included as censored observations (see Materials and Methods), the Csectioned and control women did not differ statistically with respect to the distribution of time between the two births (Table 2). The proportion of women who wanted to have their next pregnancy earlier than it actually occurred was higher among the C-sectioned women (P < 0.01; see Table 5), which suggests that the C-sectioned women had more problems in conceiving. Women who were able to have children at the date of the interview were asked the following questions to determine the number of additional births they intended to have in the future: "Looking to the future, do you (and your husband) intend to have a(nother) baby at some time? How many (more) do you intend to have?" The total

number of births intended is the number of births that had already occurred plus the future births intended. The mean number of additional intended births {after the interview) was lower among the C-sectioned than the control women, and so was the total number of children intended, especially among black women. The fecundity status8 of C-sectioned and control women differed substantially (Table 3). Only 55% of the C-sectioned women, but 71 % of the control women, were fecund; i.e., they were apparently able to have further children (with their current husbands if they were married). The more live births the woman had had, the greater the proportion of nonfecund women. But in each of these subgroups the percent fecund was lower among the C-sectioned women. For example, among women who had had two live births, 45%

Table 3. Fecundity of the Women or the Couple, if Currently Married, at the Time ofthelnterview, by Race All womena C-sectioned Control (n

Fecund Subfecund Long interval or nonsurgically sterile Surgically sterile Total

= 406)

(n

= 406)

Blackb C-sectioned Control (n

X2

(n

= 182)

(n

= 224)

(n

= 224)

%

%

%

%

%

%

55 10 3-

71 3 2

56 9 4

75 3 2

55 10 1

69 3 1

32

24

31

20

34

27

100

100

100

100

100

100

28.95, df = 3, P < 0.001. = 16.14, df = 3, P < 0.001. cIncludes also women of races other than Caucasian and black; X2 a

= 182)

Caucasian' C-sectioned Control

=

b X2

Vol. 43, No.4, April 1985

= 14.25, df = 3, P < 0.001.

Hemminki et al.. Cesarean section and subsequent fertility

523

of the C-sectioned and 72% of the control women were fecund (P < 0.001). Also, more C-sectioned than control women were subfecund (it is difficult, but may be possible, for the woman and her current husband to conceive and/or carry a pregnancy to term) (P < 0.001). Subfecundity consisted of different problems. The most common reason for subfecundity among the C-sectioned women was that it was "dangerous for her to become pregnant again" (4.4% of the C-sectioned women as compared with 0.3% ofthe control women, P < 0.001). The reason "difficulty getting pregnant" was given by 3.4% of the C-sectioned and 2.0% of the control women. The differences in fecundity status between the C-sectioned and control women were found among both Caucasian and black women. The proportion of women who had had a spontaneous abortion after the first child did not differ between the C-sectioned and control women (Table 2). To take into account the uneven occurrence of sterilization (see later), incidence rates were also calculated (the number of abortions was divided by the number of person-years, the end of follow-up being the sterilization or the interview). Among C-sectioned women, the rate was 2.7 abortions per 100 person-years and among control women, 2.4.

The C-sectioned women were more often sterilized, for both contraceptive and other reasons, than the control women (Table 4). They were also sterilized at a somewhat younger age, although this difference was not statistically significant. Only one C-sectioned woman was sterilized at the time of the first birth. When all women were included, the median interval from the first birth to the sterilization, either female or male, was shorter among the exposed than among the control women. If only couples actually having experienced sterilizations were included, the mean from the first birth to sterilization was 5.6 years among exposed women and 6.4 years among control women (P = 0.15). The most common form of female sterilization was tubal ligation (84%). However, 15% of female sterilizations were hysterectomies. The same proportions (44%) of both C-sectioned and control women said that they thought they might in the future use either female or male sterilization after they had had all the children they wanted to have (Table 4). The wantedness of the next pregnancy after the first child differed between the C-sectioned and control women, and more so among Caucasian than among black women (Table 5). More pregnancies in the control group were reported to

Table 4. Surgical Sterilizations by Race All women C-8eCtioned Control

Surgically sterile at time of interview (%)b Woman for contraceptive reasons (%) Woman for other reasons (%) Husband (%) Mean age when sterilized (yrs)" Estimated median interval from first birth (yrs! Desire for reversal (%)" Definitely (%) Maybe (%) Plans for future sterilization

Black C-sectioned Control

Caucasian" C-sectioned Control

33

24c

31

20d

34

27

19

12C

22

13d

16

11

10 4 26.9 10.0

6d 6 27.8 12.!¥"

9 1 25.3 10.6

6 1 26.4 12.!¥"

11

5 28.2 9.5

5d 9 28.7 12.1

35 15 20 44

23 13 10 44

44 17 27 41

31 17 14 42

29 14 15 48

19 11

7 46

(%)i

"Includes also women of races other than Caucasian and black. bpercent of couples if the woman was currently married. cp < 0.01. dp < 0.05. "Only sterilized women. fAll women are included; those not having a sterilization are included as censored observations; the P value refers to the Mantel-Cox statistic. lip < 0.001. hIncludes also husband sterilizations; denominator includes sterilized women/couples. iIncludes also husband sterilizations; denominator includes all women.

524

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Table 5. Wantedness of the Pregnancy Subsequent to the First Child All womena C·sectioned Control (n = 254) (n = 251) Wanted sooner On time Too soon Unwanted Indifferent, missing data Total

C·sectioned (n

(n

= 107)

Caucasianc C-sectioned Control (n = 138) (n = 144)

%

%

%

%

%

%

10 44 28 16 2

3 53 30 12 2

.6 39 30 23 2

2 40 34 22 2

14 47 27 10 2

4 63 26 5 2

100

100

100

100

100

100

13.11, df = 4, P < 0.05. X b X2 = 2.66, df = 4, not statistically significant. cIncludes also women of races other than Caucasian or black; X2 a

= 116)

Control

2 =

have occurred at about the time they were wanted ("on time"), whereas more pregnancies in the Csectioned group occurred later than wanted. When the exposed and control groups were adjusted for years of education, using multiple logistic regression, the difference with regard to the proportion of children who had arrived on time was no longer statistically significant. This is because low education and "on time" pregnancies correlated negatively with each other, and among the C-sectioned women there were somewhat more women with less education. Fifty-three percent of the C-sectioned and 47% of the control women said they wanted to have further children (Table 6). However, C-sectioned women are less likely to be able to carry out those desires, because more C-sectioned women had fecundity impairments that made it difficult or impossible for them to have children (16% versus 7%; Table 3). These patterns were similar for Caucasians and blacks. Induced abortions were not common among Csectioned women. Only one woman (in the control

=

13.02, df = 4, P < 0.01.

group) had adopted a child after the first child. Of the sterilized women (couples), 35% in the C-sectioned group and 23% in the control group wanted to have the sterilization operation reversed (Table 4). When the C-sectioned and control women were compared in the four subgroups by the date of the first birth, similar patterns to those described in Table 2 emerged (Table 7). The differences were larger in the groups of the two earlier time periods and smaller in the two later groups, probably because of varying follow-up times. Because of the small number of women in each subgroup, most of the differences were statistically nonsignificant. But the difference in the median interval between the first birth and the next live birth between the C-sectioned and control women was largest among women having their first child between 1968 and 1972 (median, 4.3 years versus 3.3 years; P < 0.05). The proportions of fecund women were notably lower in the groups of the two earlier time periods than in the later groups (Table 7). This difference

Table 6. Plans for Further Children at the Time of the Interview, by Race All womena Control C-sectioned

Intends Would like to d Does not intend Does not want to d Undecided, no information Total 18.67, df

Caucasian C-sectioned Control (n = 224) (n = 224) C

(n = 406)

(n = 406)

%

%

%

%

%

%

37 16 22 20 5

40 7 27 18 8

38 14 23 21 4

43 8 30 14 5

35 17 22 19 7

37 7 24 21 11

100

100

100

100

100

100

4, P < 0.001.

a X2

=

b X2

= 9.12, df = 4, P > 0.05.

=

Black b C-sectioned Control (n = 182) (n = 182)

cIncludes also women of races other than Caucasian and black, X2 = 13.49, df = 4, P < 0.01. dIncludes also those for whom it is impossible or unlikely to have further children. Vol. 43, No.4, April 1985

Hemminki et al. Cesarean section and subsequent fertility

525

Table 7. Comparison of the Exposed and Control Women in the Four Time Periods1 <1968

C-sectioned (n = 33)

No. of pregnancies (mean) No. of live births (mean) Total no. of intended births (mean) Fecund (%)b Subfecund (%)b Surgically sterile (%)b Subsequent pregnancy on time (%) Subsequent pregnancy wanted sooner (%) Intends further children

1.75 1.36 2.41

1968-72

Control (n =

32)

2.34 1.81 2.88

C-sectioned (n =

61)

1973-77

Control (n = 60)

1.36 1.00 2.15

1.93a 1.52a 2.70a

C-sectioned (n =

120)

1.34 0.93 2.37

1978-83

Control (n =

119)

C-sectioned (n =

1.25 0.87 2.43

68a

192)

0.51 0.33 2.25

Control

(n = 195)

0.57 0.33 2.46

9 9 76 47

25 3 69 48

30 8 56 38

43 2 53 60c

48 7 43 48

3 26a 53

76 12 12 40

90 3 6 50c

10

7

10

2

12

3c

8

3c

0

3

8

12

25

33

24

16

26

12c

24

lOa

59

59

6

3

(%)

Would like to have further children (%)

ap < 0.01. bCouple, if the woman is currently married. cp < 0.05.

can be largely attributed to surgical sterilization. The proportions of sterilized women or couples were more similar between C-sectioned and control groups (relative differences) in the two earlier time periods than in the two more recent time periods. The differences with regard to the wantedness of the next pregnancy given in Table 5 could be seen in all four subgroups by the date of the first birth. Also, the greater proportion of C-sectioned women who would like to have more children, but who were apparently unable to have them, could be seen in all subgroups by the date of the first birth (Table 7). The proportions of women who intended to have further children were higher among the control women in all subgroups except the most recent one; however, the differences were not statistically significant. Because the C-sectioned and control women differed somewhat with regard to some background variables (Table 1), the adjusted odds ratios were computed with multiple logistic regression for some of the key categorical outcome variables (female sterilization, fecund, subfecund, and the next pregnancy after the first child was on time). Adjustments were made for years of education, whether Catholic or not, whether Hispanic or not, whether living in a central city or not, and whether living in another metropolitan area or not. Only one odds ratio was influenced by adjustment: the odds ratio of planned status of the next pregnancy was influenced by adjustment for education (see above). Mean differences between 526

the C-sectioned and control women for the continuous outcome variables (mean number of pregnancies and live births after the first child and the additional and total number of births intended) were also adjusted with multiple regression analysis with the same four confounding variables. The differences of means between the Csectioned and control women became slightly larger after adjustment, but no difference previously nonsignificant became statistically significant. DISCUSSION

The actual and intended numbers of children were somewhat lower among women who had had a cesarean section in their first delivery than among the control women. This finding, and the size of the difference, is in accordance with previous studies. 3 • 4 Unlike these previous studies, this study showed essentially no difference in the proportion of women who by the time of the interview had had at least one subsequent child after the first child. In this study, control women intended to have more total births than C-sectioned women, because control women were more likely to have had third or later births than C-sectioned women and more likely'to intend to have additional births. The available indicators in the study suggest that the desire for children was not less among the C-sectioned women than among their controls: at least as many C-sectioned as control women wanted more children, induced abortions

Hemminki et al. Cesarean section and subsequent fertility

Fertility and Sterility

were not more common among C-sectioned women, and many wanted sterilization operations reversed. The difference in the number of children seems to result from physical difficulties in having subsequent children after a cesarean section. In the C-sectioned group there was a larger proportion of women who were sterilized and a larger proportion who had difficulties in conceiving or carrying the pregnancy to term. We could not judge clearly from the data available whether the greater number of sterilizations among C-sectioned women was due to assumed greater need (e.g., because of assumed dangers of pregnancies following cesarean sections), convenience of a sterilization operation after cesarean section, or diminished desire for further children. But considering the smaller number of male sterilizations and the greater number of women in the C-sectioned group who wanted to have their sterilization operation reversed, the convenience of the operation may have resulted in some sterilizations that were later regretted. Because there seemed to be little difference between the C-sectioned and control groups in the proportions of women or couples who ultimately would be sterilized (Table 4), the difference between the different time periods (Table 7) may derive from how early in their reproductive career the C-sectioned and control women are sterilized. Nationwide statistics from the United States have shown a rapid increase in sterilization. 9 Also, sterilization commonly is done in connection with cesarean section, especially in multiparous women. 1O- 12 In this study, only one woman was sterilized in connection with the first delivery, but many sterilizations may have been done during later deliveries. All the information for this study was obtained by interviewing the women themselves. Most of the information used in this study concerned concrete life events and is appropriate for interview studies. Even the induced abortions following the first birth seem to have been relatively well reported. In 1980, the nationwide ratio of reported induced abortions to live births was 0.20 among women who had had one previous live birth and 0.30 among those who had had two or three previous live births. 13 The ratios in this study were 0.22 for C-sectioned and 0.25 for control women (Table 2). The opinions and attitudes were interpreted by assuming that there was no bias in reporting by the exposure status, i.e., whether the woman had undergone cesarean section or not. Vol. 43, No.4, April 1985

There was no evidence of such bias, and no reason to believe that such bias exists. Studying the effects of cesarean sections on fertility is difficult, because selection for the operation is difficult to overcome. It may be that factors which led to the operation are responsible for the differences in later fertility. But women with strong and rare confounding factors were excluded from the study (see Materials and Methods), four major known confounding factors were taken into account by matching, and multivariate adjustment by differing background variables had little effect upon the results. Also, an earlier comparison oftwo cohorts from different exposure rates in Sweden4 suggests that the operation itself, and not only the selection for the operation, contributes to the differences. In summary, the results of this study suggest that cesarean section at the first birth may lead to reduced subsequent fertility. For most indicators offertility, the lower fertility could be seen in the two racial groups as well as in the different time periods. The lower fertility seems to be attributable to physical problems associated with the operation, and possibly caused by the operation itself, and not to inherently different opinions and attitudes toward pregnancies and children.

Acknowledgments. We want to thank Mr. Joseph D. Farrell and Ms. Virginia Brainard for their help in creating the data tapes on which this analysis is based, and Ms. Denise Belton and Ms. Dorothy Day for their help in typing the manuscript.

REFERENCES 1. Placek PJ, Taffel S, Moien M: Cesarean section delivery rates: United States, 1981. Am J Public Health 73:861, 1983 2. Geller H-F, Herlyn U: Nachwirkungen der Sectio caesarea. Zentralbl Gynakol 19:657, 1964 3. Zdeb MS, Therriault GD, Logrillo VM: Frequency, spacing, and outcome of pregnancies subsequent to primary cesarean childbirth. Am J Obstet Gynecol 150:205, 1984 4. Hemminki E: Unpublished data 5. Pratt WF, Mosher WD, Bacharach CA, Horn MC: Understanding U.S. fertility: findings from the National Survey of Family Growth. Popul Bull 39:4, 1984 6. Mosher WD: Fertility and family planning in the 1970's: the National Survey of Family Growth. Fam Plann Perspect 14:314, 1982 7. Kalbfleisch JD, Prentice RL: The Statistical Analysis of Failure Time Data. New York, John Wiley & Sons, 1980, p 10

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8. Mosher WD, Pratt WF: Reproductive impairments among married couples: United States. Vital Health Stat [23), No. 11, 1982, p 5 9. Cypress BK: Use of health services for disorders of the female reproduction system: United States 1977-78. Vital Health Stat [13), No. 63, 1982, p 19 10. Mosher WD, Keppel KG: Social and clinical correlates of postpartum sterilization in the United States, 1972 and 1980. Public Health Rep 99:128, 1984

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11. Placek PJ,Taffel SM, Smith JC, Maze JM: Postpartum sterilization in cesarean section and non-cesarean section deliveries: United States, 1970-75. Am J Public Health 71:1258, 1981 12. Centers for Disease Control: Surgical Sterilization Surveillance 1979-1980, 1983, p 14 13. Centers for Disease Control: Abortion Surveillance 19791980, 1983, p 34

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