Postvasectomy residual sperm pregnancy.

A pregnancy occuring within a few months after a successful vasectomy is sometimes attributed by a skeptical physician to sexual involvement by the spouse with a nonvasectomized man. This assumption may be unjustified because of the fact that after a vasectomy, some residual sperm which are viable enough to cause pregnancy could remain stored distal to the site of occlusion. The Maternal and Child Health Center of Taiwan documented a case history of a 32-year-old father of 2 who impregnated his wife approximately 38 days, and at least 9 ejaculations, after a successful vasectomy. The patient had no urogenital abnormalities and had an uneventful vasectomy procedure. He resumed intercourse with his wife 8 days after vasectomy and returned for 5 semen tests during the year after vasectomy. The patient's 28-year-old wife had her last menses 24 days after the vasectomy, and pregnancy test 57 days after the vasectomy confirmed the suspicion of pregnancy. Vacuum aspiration terminated the pregnancy 2 days later. There was no doubt or question at all that the patient was his wife's only sexual partner. The authors concluded that based on examination of several thousand postvasectomy semen specimens, the distribution of the biologic limits for residual sperm viability is an asymmetrical distribution skewed to the right, suggesting that the limits may even exceed 38 days for some individuals. Thus physicians should be careful in evaluating a pregnancy which occurs a few months after a successful vasectomy.