Expert Commentary

The effect of oral contraceptives on conception

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Does prolonged use of oral contraceptives delay planned conception?

Past studies

Several earlier studies have shown that women who stop oral contraceptives (OCs) have a short-term decrease in fertility that begins the first month after discontinuing use and lasts up to a year. It took 3 months to several years for pregnancy rates to equal those of comparison groups.1-5

A smaller study of women discontinuing associated with longer intervals from discontinuation to conception.6 Additional investigations have shown a decrease in fertility rates after OCs, but have not controlled as well for other factors such as age (OC users tend to be older than non-users). Still, multiple studies indicate that the rate of post-pill amenorrhea is low, and therefore unlikely to affect pregnancy rates.7-8

This study

This investigation is part of a larger study of environmental and genetic influences on pregnancy outcome. The study enrolled 85% of couples in southwest England expecting a child during the study period. Researchers collected information on various aspects of the women’s health, including tobacco use, alcohol consumption, body size, and occupational and educational status. The study population included a total of 12,106 couples—8,497 of which had planned pregnancies.

Researchers found the pregnancy rate at 1 year was significantly higher for OC users than for non-users. Although the absolute difference was not large (89.5% of women using OCs for more than 5 years versus 85.4% of never-users), it is consistently related to the length of exposure. Stepwise regression analysis showed that the higher pregnancy rates persisted even when other factors, such as smoking and maternal age, were considered.

Find this study

Farrow A, Hull MGR, Northstone K, Taylor H, Ford WCL, Golding J. Prolonged use of oral contraception before a planned pregnancy is associated with a decreased risk of delayed conception. Human Reprod. 2002;17:2754-2761.

Who may be affected by these findings?

Current OC users planning future pregnancy.

Expert commentary

The ideal contraceptive would be highly effective and readily reversible; planned pregnancy would not be delayed or prevented. However there are persistent beliefs that women need a break from prolonged use of OCs before they are able to conceive. Post-OC amenorrhea is presented as a usually reversible complication of OC use that may delay conception. Unfortunately, the alternative may be a contraceptive with a higher failure rate (leading to unplanned pregnancy) or one with fewer noncontraceptive benefits.

The women in the comparison group included users of other contraceptives as well as women who used no contraception at all. Other studies of post-OC fertility have used various comparison groups. Several have suggested that OCs may decrease the rate of upper genital infection.9,10 Thus, OC users may have a higher subsequent fertility rate, since users of nonhormonal methods may experience more tubal infertility.

The current study does not demonstrate a dip in fertility, but it doesn’t address the possibility of a short-term decrease with prompt recover y. Still, the findings strongly support the thesis that pregnancy rates for women who stop OC use are the same, if not higher, than rates for women using no contraceptives or another birth control method.

Bottom line

Women who want to become pregnant should discontinue contraception when they are ready, and OC users shouldn’t anticipate a longer period from discontinuation to conception.

Dr. Borgatta reports no financial relationship with any companies whose products are mentioned in this article.

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