Sperm FAQ

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 them to get pregnant are extremely low.

When sperm are inside women'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 they 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 men ejaculate they release 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:

• Don't smoke or use illicit drugs, especially anabolic steroids.
• Avoid contact with toxins such as pesticides and heavy metals.
• Limit how much alcohol you drink.
• Eat a healthy diet and keep your weight under control.
• Keep your scrotum cool, because heat slows down the making of sperm. To do this, avoid hot baths, wear boxers instead of briefs, and try not to wear tight pants.

What does a semen analysis tell?

It's a test that can help your doctor figure out why you and your partner are having trouble having a baby.

Some things you can learn from the analysis:

Amount and thickness of semen. On average, each time men ejaculate they release 2-6 milliliters (mL) of semen, or around a 1/2 teaspoon to 1 teaspoon.

Less than that amount may not contain enough sperm for a woman to get pregnant. On the other hand, more than that could dilute the concentration of sperm.

Semen should be thick to start with and become thinner 10 to 15 minutes after ejaculation. Semen that stays thick may make it difficult for sperm to move.

Sperm concentration. Also called sperm density, this is the number of sperm in millions per milliliter of semen. Fifteen million or more sperm per mL is considered normal.

Sperm motility. This is the percentage of sperm in a sample that are moving, as well as an assessment of how they move. One hour after ejaculation, at least 32% of sperm should be moving forward in a straight line.

Morphology. This is an analysis of the size, shape, and appearance of sperm.

Do men stop making sperm when they're older?

Men can continue to be fertile throughout life. The amount of sperm you make goes down as you get older, but even elderly men have fathered children.

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