It seems like an easy thing to get that sperm to meet an egg, but, according to a new video from the Science Channel, that little sperm's journey is a lot more difficult than it seems.
While the basics of the trek are outlined in any general health class, the specifics are pretty fascinating. First, in one ejaculation, there are about 280 million sperms, which is a lot of competition. If they're ejaculated into a vagina (and not thwarted by a condom), they'll make their way upward. But, along the way, 210 million of them will drop out of the running due to some, uh, difficulties: Some may have two heads, others might be dealing with three tails, while others may not have a tail at all. Those that are able to do so head into the cervix where the mucus, which is so helpful in keeping out bacteria, also keeps out many of those little sperm.
Then comes the uterus, where immune cells fight to keep the foreign organisms out. By the time they reach the fallopian tubes, only about 200 sperm are left. And, as the video notes, half of them will swim up the wrong tube. Of the 100 that choose the right path to meet a fertile egg, only the fastest one will actually fertilize it. When that happens, a chemical message seals the egg off from other potential suitors.
So, although sperm don't have to go too deep to start the journey, they've still got a long way to go to see the deal. This isn't to say you shouldn't take precautions: In some cases, pregnancy can occur even when semen is placed on the vulva or simply near the vaginal opening. However it happens, though, just remember that you were created from the fastest sperm — you were a winner from day one.