Oral contraceptives and ovulatory causes of delayed fertility.

The return of fertility for women who discontinue oral contraceptives takes longer as compared with women who discontinue other methods of contraception. It remains unclear, however, whether subsequent fertility differs according to duration or age at first use. The authors performed a nested case-control study within a cohort of 116,686 female registered nurses residing in 14 US states. Baseline information was reported on mailed questionnaires in 1989. Cases comprised 1,917 married nurses without previous pregnancy who were unable to become pregnant for at least 1 year and were subsequently diagnosed with primary ovulatory infertility. Controls comprised 44,521 married parous nurses with no history of infertility and no pregnancies lasting less than 6 months. After allowing for 2 years of suppressed fertility following discontinuation of oral contraceptive use and excluding women with signs of menstrual or hormonal disorder, the authors found that the multivariate relative risk for ovulatory causes of delayed fertility was 1.2 (95% confidence interval 0.7-1.9) for ever users. There was no statistically significant trend of increasing risk with increasing duration of use and younger age at first use. The fact that 88 percent of cases reported an eventual pregnancy by 1993 suggests that absolute fertility was not impaired.