The effects of recent oral contraceptive use on the outcome of pregnancy.

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.