What drives pregnancy rates after vasectomy reversal? Lots of things. The judgment and skill of the surgeon are critical as not all surgeons are the same. Two operations are possible during reversal surgery (vasovasostomy or epididymovasostomy) and choosing the correct one for each side of each patient involves deft surgical judgment. After the type of procedure is chosen, the skill comes in making it all work in some of the smallest organs in the body. To provide perspective, the suture used for this surgery is about 1/5 the size of a hair and is not easily visible to the human eye. The tubes to be reconnected are about 1/10 of a millimeter in diameter (100um) and can test the absolute limit of controllable hand motion (2-3 um). Doing this right takes training, experience, focus, control and good jazz in the operating room. The result is a “patency” rate, or sperm in the ejaculate.
But even with sperm returning to the ejaculate, the natural pregnancy rates are not the same as those in couples without a vasectomy reversal. Why? Think of it this way, you measure your surgeon by the patency rate, which is a technical issue. However, pregnancy rate is a biological outcome that involves many more variables. For example, we have published that female fertility potential is the single most important factor in pregnancy success after reversal. Since it can take up to a year after vasectomy reversal surgery to conceive, I recommend that female partners >35 years of age consider an evaluation of their fertility potential (i.e. get an answer to the question: “Do I have a year of time to conceive?”); I insist that women 37 years of age consider this evaluation and with a stern gaze, I very strongly recommend that women >40 years of age undergo this evaluation. I do this because my goals are aligned with those of patients: at the end of the day, my greatest reward is a holiday card with a kid in it.
Say that the sperm counts are good after reversal and the female partner is young. Why wouldn’t this couple conceive after reversal? Technically, a 30-year-old woman trying to conceive with an unvasectomized partner has a mean cumulative fecundity (pregnancy) rate at 1 year of about 85%. With a vasectomized and reversed male partner, this rate is about 65%. Not a huge difference but a real one.
To explain this, we need to introduce the immune system. Men who have a vasectomy essentially become “inoculated” to their sperm, similar to a mumps or flu vaccine. The immune system actively develops antibodies to sperm and this reaction eventually wears off with time. But, the immune system also has a fabulous memory, for which we are all grateful. Hence, at the time of vasectomy reversal, the immune system becomes inoculated again and antibodies to ejaculated sperm are generated. All things being equal, antisperm antibodies are likely the reason why pregnancy rates after vasectomy reversal are lower than expected. Since the immune response after reversal also wears off with time, this may also explain why it takes longer to conceive after vasectomy reversal.
What’s so incredible about all of this biological and surgical action and reaction, is that gobs of beautiful babies are more likely than not to be the result. Someone, somewhere has prioritized reproduction in the grand scheme of things. As Thoreau said: “Nature is full of genius, full of divinity; so that not a snowflake escapes its fashioning hand.” A toast to the beauty of biology.