Fetal loss, twinning and birth weight after oral-contraceptive use.

To evaluate the effect of oral-contraceptive use on subsequent offspring, I reviewed information on the pregnancies of 19,887 women who indicated, in response to a mail questionnaire, that they had used oral contraceptives. The rates of spontaneous abortion and stillbirth were smaller for former users than for nonusers--a finding consistent with previous studies. Twinning was more frequent among births of infants conceived soon after cessation of oral contraceptives, the rate being approximately twice the expected value for women who had used oral contraceptives for more than six months (P = 0.1). The sex distribution of the twins indicated that the increase was mainly in dizygous twins (P = 0.02), in accordance with predictions about increased twinning after cessation of oral contraceptive use. No relation was evident between oral contraceptive use and birth weight.