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RESUMEN

Of 10479 singleton pregnancies in South Glamorgan between January 1974 and June 1976, 27.3% occurred in women who had used oral contraceptives in the 3 months prior to their last menstrual period (users) and 72.7% occurred in women who had not used oral contraception during the same period (non-users). Significantly more users gained weight excessively. Oral contraceptive use increased the likelihood of uncertain dates and post-maturity. The incidence of neural tube defects was higher among children born to users, although the overall perinatal outcome was not adversely affected. The sex distribution of the offspring was the same in both groups.

PIP: 2859 (27.3%) of the 10,479 singleton pregnancies registered in South Glamorgan, Wales, between January 1974 and June 1976 occurred in women who had used oral contraceptives (OCs) in the 3 months prior to their last menstrual period. Excessive weight gain during pregnancy was documented in 499 (25%) of the OC users compared to 1391 (23%) of nonusers--a significant difference. 20% of OC users versus 18% of nonusers had uncertain gestational dates. The perinatal death rate was not significantly different--16/1000 births among OC users and 17/1000 among nonusers. However, the incidence of neural tube defects was significantly higher among users (0.63%) than among nonusers (0.25%). Finally, there was no significant difference between the 2 groups in mean birthweight and the sex of the infant was not affected by OC use. Overall, these findings fail to document any significant deleterious effects of OC use immediately before pregnancy. However, a pill-free interval is recommended prior to allow the menstrual cycle to return to normal so that gestation can be assessed accurately.

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RESUMEN

Of 10 479 single births in South Glamorgan between January 1974 and June 1976, 27.3 per cent of infants were born to women who had used oral contraception in the three months prior to their last menstrual period (users) and 72.3 per cent were born to women who had not used oral contraception during the same period (non users). There were significantly more infants with neural tube defects among users compared with non users. Abnormalities of the digestive, genito-urinary and cardiovascular system, bones, muscle, skin and connective tissues, endocrine glands, blood chromosomes and oral clefts, were of similar incidence in the two groups.

PIP: All women normally resident in the city of Cardiff and towns of Barry and Penarth who delivered a single child between January 1974 and June 1976 were studied retrospectively as a cohort to study without bias the effects of recent oral contraceptive use on the fetus. There were 10,479 births (single) during the period under study. Of these, 2859 (27.27%) were born to users and 7620 (72.72%) were to nonusers. Other factors compared, which were known to influence the incidence of malformation, were maternal age, parity, social class, and the smoking habit. 2.83% (n=81) infants were born with abnormalities among users and 2.95% (n=225) had abnormalities among nonusers (difference not significant). Users are defined as those who took oral contraception in the 3 months before their last menstrual period. 3 babies had Down's syndrome among users but there were no other chromosomal abnormalities in this group; however, a total of 14 nonusers' babies had chromosomal abnormalities (10 Downs and 4 others). 18 infants had neural tube defects among users and 19 among nonusers. Age, parity, social class, and smoking were not significantly different among those users and nonusers who had a baby with neural tube defect. Overall, incidences of abnormalities were similar except for neural tube defect, which was statistically significantly higher among users (.63% in users vs. .25% in nonusers).

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