After having a baby, one of the many things that couples often consider is how to prevent, or delay, a subsequent pregnancy. Couples may not like barrier methods, such as condoms, leading to the option of internal methods. This focuses the intervention on the woman, because oral contraception –the pill– has a track record of many decades with an excellent effectiveness and safety profile. There are many formulations of oral contraception, plus several types of intrauterine devices (IUD), but not everyone tolerates these methods, so for a long time there has been a quest to develop a contraceptive for men analogous to the female pill, or at least to the IUD.
It’s a pretty tall order, because male fertility works very differently from female fertility. The latter depends on a few processes that are fairly easy to head off at the pass. For one thing, a woman releases just one egg every month from one of her two ovaries. Known as ovulation, that process of releasing an egg depends on a the balance of just a handful of hormones, as does the implantation of a fertilized egg into the lining of the uterus and further development of the pregnancy. Hormonal tricks involving tiny doses of hormones in the pill can sabotage these processes, rendering a woman temporarily infertile without stopping the influence of female hormones on her secondary sex characteristics –visible signs of gender that make women and men appear different. A similar logic applies to an IUD; it can prevent an early embryo from implanting in the uterine lining, because implantation is a fairly challenging to do in the first place. Usually, only one early embryo (two in the case of twins) is trying to implant, so by disrupting the uterine, the IUD stands a good chance at winning out.
With men, on the other hand, there are hundreds of million of sperm cells that potentially can be chasing after one healthy egg. Interfere with that egg with female contraception and the status of those hundreds of millions of sperm doesn’t matter. But if the strategy is contraception through the man, it has to affect hundreds of millions of cells all at once, which really means billions of cells over the course of a monthly cycle that for the woman involves just one cell, which is to say that one egg. As for interfering with the hormonal process of making the sperm in the first place, that sounds good on paper, but the genesis of sperm is much difficult to isolate from the rest of male physiology the way that ovulation can be isolated from a female physiology with the hormonal tricks.
Now, if we’re talking about permanent sterilization, that’s actually easier to do in a male than a female. Urologists can simply cut the vas deferens, the tube through which the sperm travels from the testicle, but that’s not a good solution for a couple that merely wants to delay the next pregnancy. This has brought the focus of male contraception research to the goal of modifying different parts of sperm through specially-designed drugs, genetic modification, or other approaches, but this is still years in the future, perhaps decades. In the meantime though there’s another technique in the works, called VasalgelTM. If you don’t want something to get through a tunnel, you can sever the tunnel, but you also could plug it, and that’s Vasalgel approach. What would happen is that a special polymer gel would be injected into the vas, where it would harden and form a plug that would be effective for years. But, it could be reversed at any time, by injection of another substance that dissolves the gel. Clinical trials are not happening yet, but new research on monkeys found the method extremely effective.