For some women, the thought of having a baby fills them with immediate joy. For others, the timing may not be right, and the thought of a pregnancy is downright scary. It only takes one microscopic sperm to start the ball rolling, which means it only takes a small amount of semen to get pregnant.

Size

Millions of sperm are in just 1 tbsp. of semen, according to the Menstuff website. In fact, the average amount in one ejaculation is between 40 million and 600 million. The average amount of semen ejaculated is about one-half teaspoon. With all those sperm swimming around, the odds are good for most women that at least one of them will be able to reach the egg, if there is an egg present.

Function

The function of semen, which is the fluid that contains sperm, is to transport and protect the sperm until one of them can fertilize the egg. It only takes one of the millions of sperm that make up the semen to fertilize the egg. In fact, only one sperm is even allowed to fertilize the egg. Once the lone sperm breaks through the egg’s wall, the egg then releases a special hormone that prevents any other sperm from entering the egg. The sperm then works its way to the center of the egg, where fertilization occurs.

Speed

Sperm are fast swimmers. It only takes 90 seconds from ejaculation for them to reach a woman’s cervix, according to the Dr. Spock website. This means that not only do you need a single sperm to become pregnant, but the sperm can enter the “danger zone” quickly. For that reason, and because sometimes sperm are present in pre-ejaculation fluid, using the “pull-out” method of birth control is not recommended.

Time Frame

Sperm have a single-minded goal of fertilization, and they are designed specifically for that purpose. Fertilization of the egg can occur as quickly as five minutes after ejaculation, according to Dr. Spock. In addition, sperm can live for up to three days inside the fallopian tubes, where the egg rests after being released from the ovary.

Pregnancy

Just because a sperm cell is able to fertilize an egg does not necessarily mean that pregnancy will occur, however. The egg must successfully travel down the fallopian tube and implant into the lining of the uterus. This journey and implantation can take up to seven days, and several things can prevent implantation from occurring successfully, including a problem with the egg itself, or issues with the lining of the uterus.