Ask Dr. H: Vasectomies can fail at some point

Question:

I recently got married to a man who had a vasectomy 21/2 years ago in a previous marriage. Well, I'm pregnant! My husband initially accused me of cheating on him, but I swore to him that I've not been with another man. It must be that his vasectomy failed. But how can that be? Aren't they permanent?

Answer: While a vasectomy is a highly effective method of birth control, it is not 100 percent effective. In fact, 2 in 1,000 vasectomies will fail at some point. This happens when the sperm-carrying tubes rejoin naturally.

How can this happen? Well, there's such a powerful force in nature driving the perpetuation of our species that, despite our attempts to limit our individual reproduction, our own body seeks to thwart such efforts. It's an amazing thing that surgically cut and tied off reproductive tubes can actually grow back together.

Urologists will tell you that upward of one-third of all men who undergo a vasectomy assume that their vasectomies were a success and do not submit semen for analysis at six and 12 weeks. However, even when the "all-clear" signal is given, a very small risk of failure exists and can occur at any time (as you've discovered). I'd therefore suggest that a semen analysis be done periodically to ensure that no sperm have returned - indicating a failed vasectomy.