How Does the Egg Get Fertilized?

How Does the Egg Get Fertilized?

A woman’s body releases one egg every month during her menstrual cycle. This is known as ovulation. Ovulation usually occurs 14 days before a period. If this egg is fertilized, the woman becomes pregnant. If it is not fertilized, the egg passes out of her body with her next period.

Below, we discuss the process and steps involved in the fertilization of egg

Ovary to the Fallopian Tube

When the ovaries release an egg, it moves into the fallopian tubes. It then waits here for about 24 hours to be fertilized. To conceive, sperm must fertilize the egg within this window. Sperm can live inside the woman’s body for up to 5 days so even if the couple has unprotected sexual intercourse a day or two before ovulation, the woman may become pregnant.

The Journey of the Sperm

At a time, the semen a man ejaculates contains millions of sperms. Only one of these sperms is needed to fertilize the egg. Once released in the woman’s body the sperm start swimming through the cervical mucus towards the fallopian tubes. The sperm can take anywhere between half an hour to more than 24 hours to reach the fallopian tubes. Not all the sperm released can reach the fallopian tubes as many will die along the way.

Fertilization of Egg

Only one sperm can enter the egg’s protective layer. The protective membrane is known as the zona pellucida. It serves two functions – firstly contains sperm receptors that are specific to human sperm and secondly it makes the egg impermeable to other sperm once a single sperm has penetrated the membrane. The sperm then has 24 hours to fertilize the egg. When the sperm fertilizes the egg, it determines the genetic makeup including the sex of the fetus. If the sperm has an X chromosome, the fetus will be a girl while if it has a Y chromosome, the fetus will be a boy.

Cell Division

Once the egg is fertilized, it forms a single cell embryo known as a zygote. Over the next week, it undergoes multiple cell divisions and becomes an organized mass known as a blastocyst.


Once the embryo reaches the blastocyst stage, it begins moving towards the uterus for implantation. If the embryo is implanted in the fallopian tubes itself, it will result in a miscarriage and could be very dangerous for the mother. The health of the embryo and the receptivity of the uterus are crucial for a proper implantation on the uterine walls.