OK, so technically it only takes one sperm and one egg to make a baby. When you factor in real life, however, conception is rarely that straightforward and easy. For instance, can you get pregnant with just a little sperm? Really, what are the over/under odds on conceiving a baby with the tiniest bit of semen? It seems like a simple question, but there are many factors involved.
First, it helps to keep in mind that swimmers are generally plentiful. According to WebMD, there are around 100 million sperm are in the average male ejaculate. If that sounds like overkill, remember that the sperm has to venture through the fallopian tubes to get to the egg, and millions don't make it, as further explained in WebMD. They need lots of backup.
So how much semen is needed to produce a pregnancy? Quite a bit, in general. As explained in the Mayo Clinic, men are most likely to be fertile when their ejaculate has at least 15 million sperm in each milliliter. To put this in perspective, a teaspoon contains about 5 milliliters. So while it may seem like a small amount of seminal fluid, as long as it contains enough sperm, then pregnancy is possible. Remember: sperm may be small, but they are legion.
If you and your SO are avoiding pregnancy, then remember that what looks like a tiny bit of fluid can contain millions of sperm. Therefore, it's smart to use birth control for any type of intercourse. If your partner is fertile, then one drop of seminal fluid inside you may be enough to create a baby. Fortunately, there are plenty of ways to make sure your birth control actually leads to safe sex.
On the flip side, what if you and your partner are trying to conceive when he has a low sperm count? Fortunately, you have many options. According to the Mayo Clinic, treatment options include surgery, medication, or even assisted reproductive technology (ART). Even men with low sperm count can father children, so you and your SO can work with your doctor to figure out your best options.