Outcome of pregnancies following the use of oral contraceptives

Abstract

The use of oral contraception by women doctors on the Medical Register for England and Wales in 1975 was studied and related to the outcome of their pregnancies. Nearly two thirds had used oral contraception at some time, but less than one third of their pregnancies had followed its use. Users tended to be younger at the time of the survey and to smoke in pregnancy more often. After allowing for these associations a poor outcome was just slightly more common in pregnancies occurring after OC use, particularly in conceptions occurring within a month or after a year of cessation. In contrast conceptions occurring in the 2nd or 3rd month after cessation had an unusually favourable outcome. It therefore seems likely that at least some of this weak association between oral contraception and poor outcome may be explained by factors that determine the length of time it takes to conceive. Overall it seems that any real risk to pregnancies conceived after cessation of oral contraception must be very small and outweighed by the undoubted advantages of its use.

PIP: The results of a survey of the outcome of pregnancies of women doctors, a proportion of whom had conceived after using oral contraception, are presented. Data on oral contraceptive use were gleaned from the Medical Register for England and Wales in 1975. Of the women doctors registered at this time, nearly two-thirds had used oral contraception at some time, but fewer than one-third of their pregnancies had followed oral contraceptive use. The survey yielded the following characteristics about women doctors who chose oral contraception: 1) they were younger at the time of the survey and 2) they tended to smoke in pregnancy more often. Allowing for these 2 associations, it was calculated that a poor outcome of pregnancy was just slightly more common in pregnancies occurring after oral contraceptive use, particularly in conceptions occurring within a month or after a year of cessation of oral contraception. In comparison, those conceptions which occurred in Month 2 or 3 after cessation of medication showed unusually favorable outcomes, leading to the conclusion that at least some of this weak association between oral contraception and poor outcome may be explained by factors that determine the length of time it takes to conceive. In general, however, the risk-benefit ratio for oral contraception seems weighted toward benefit.