MULTIPLE BIRTHS IN FORMER ORAL CONTRACEPTIVE USERS

Abstract

Multiple births were studied in a cohort of 2953 former oral contraceptive users and 13,630 controls, all the women were interviewed post partum. There were 238 multiple births, a rate of 14.4/1000 deliveries. Former oral contraceptive users had 13.5/1000 sets of multiple births compared to 14.5/1000 in the controls. When women who had received treatment for anovulation were excluded, these rates were 11.1 and 12.7/1000 respectively, a difference which is not statistically significant. There was, however, a significant deficit of multiple births among the small group of former pill users who were underweight in relation to their height at the time of conception. Multiple births were also increased after stopping sequential pills and preparations containing high doses of oestrogen, and there was an excess of multiple births following breakthrough pregnancies. These findings, although statistically significant, are based on small numbers, and require confirmation from other studies.