You may know it takes one sperm and one egg to make a baby, but if you're like most folks, you might not remember much else about sperm from biology class. If infertility is an issue for you and your partner, it helps to understand the basics.

How long do sperm live?

The answer depends on a number of things, but the most important is where the sperm are located.

On a dry surface, such as clothing or bedding, sperm are dead by the time the semen has dried. In water, such as a warm bath or hot tub, they'll likely live longer because they thrive in warm, wet places. But the odds that sperm in a tub of water will find their way inside a woman's body and cause her to get pregnant are extremely low.

When sperm are inside a woman's body, they can live for up to 5 days. If you're a man and you have sex even a few days before your partner ovulates, there's chance she may get pregnant.

How many sperm do you need to get pregnant?

It takes just one sperm to fertilize a woman's egg. Keep in mind, though, for each sperm that reaches the egg, there are millions that don't.

On average, each time a man ejaculates he releases nearly 100 million sperm. Why are so many sperm released if it takes only one to make a baby? To meet the waiting egg, semen must travel from the vagina to the fallopian tubes, a tough journey that few sperm survive. Experts believe this process may be nature's way of allowing only the healthiest sperm to fertilize the egg, to provide the best chances of having a healthy baby.

For those sperm that complete the trip, getting into the egg, which is covered by a thick layer, is far from a sure thing.

Is there anything you can do to improve the health of your sperm?

Many of the things you do to keep yourself healthy can also do the same for sperm. Try some of these tips: