How Sperm Prepare for the Big Moment of Fertilization

The sperm that shoot out of a penis during ejaculation are actually immature. Like teenagers, they still need some time to grow and develop until they’re ready to help create a baby. This growth can only happen once they leave the penis and the semen, and set out on their own.

This growth process is called capacitation, and in nature it happens as the sperm swim through the woman’s body. As they travel through vaginal fluid and cervical mucus toward the uterus, the sperm mature. By the time they reach the egg, they’re fully developed and ready for the big moment of fertilization.

Doctors used to think that capacitation could only happen in vaginal and cervical fluid. With the invention of IVF, however, scientists discovered that any simple fluid can help the sperm mature. This is why during the IVF process, doctors “wash” sperm to clean off any semen. Doctors then place the sperm in a simple laboratory fluid, where they mature. Amazingly, when sperm are placed in this special liquid, they become super-sperm, and start swimming much faster than they would in nature!

Whether swimming in the fluid of a woman’s body, or in a laboratory, after a few hours the sperm are all grown up and ready to unite with the egg. Apparently everyone—even sperm—needs to experience their own journey before they’re ready to become a great parent.