The risk of pregnancy after vasectomy.

OBJECTIVE To describe the pregnancy rates among women whose husbands underwent vasectomy. METHODS Between 1985 and 1987, 573 women aged 18-44 years whose husbands underwent vasectomy in medical centers in 5 U.S. cities were enrolled in the U.S. Collaborative Review of Sterilization, a prospective cohort study of male and female sterilization. Women were interviewed by telephone at 1, 2, 3, and 5 years after their husbands underwent vasectomy. RESULTS Among the 540 eligible women at risk for pregnancy, there were 6 pregnancies occurring from 6 to 72 weeks after vasectomy. The cumulative probability of failure per 1,000 procedures (95% confidence interval) was 7.4 (0.2, 14.6) 1 year after vasectomy and 11.3 (2.3, 20.3) at years 2, 3, and 5 [corrected]. CONCLUSION Couples considering vasectomy should be counseled about the small, but real, risk of pregnancy following the procedure and that men are not sterile immediately after vasectomy.