How Are Eggs Fertilized


The process of fertilization takes place when a follicle releases an egg from the ovary. The ovary then moves toward the entrance of the fallopian tube. During intrauterine insemination, sperm is inserted into the uterus. These sperm cells enter the fallopian tubes. Once inside the tube, they attach themselves to the fallopian tube's wall and stay there for "storage," during which they go through a maturation process that prepares them for penetrating the egg. A sperm cell that has completed this maturation process detaches itself from the wall and leaves the storage site. If ovulation took place in the previous 24 hours, releasing an egg that is ready to be fertilized, the mature sperm will go on a long, complicated journey through the tube to the site of fertilization.

After receiving an HCG trigger shot, hopefully the follicle will release the egg and meet the awaiting sperm in the fallopian tube. Sperm travels about 1/8 inch per minute but sperm is about 1/600 inch long so that’s really like a human jogging at about 4 miles an hour. Getting the sperm inserted through an IUI speeds up this time because the sperm is inserted directly into the uterus.  The egg can only be fertilized for about 18- 24 hours after it is released, so sperm must be present in the fallopian tubes around the time of ovulation. Sperm can usually survive for around 3 – 5 days in the woman's reproductive tract. This is why fertility specialists have to delicately time a woman’s ovulation in sync with insemination.

Millions of sperm are needed in each sperm sample due to the fact that thousands of sperm swim in the wrong direction, some swim in circles and some don’t swim at all, they hang back and wait. Scientists say that during sexual intercourse, that only about 2,000 sperm are released during ejaculation. Purchasing your own sample of sperm increases the chances of getting pregnant.

If the egg is not fertilized it will die and two hormones called progesterone and estrogen levels will drop. Without these the uterus lining breaks up and is released through the vagina. When this happens, your “period” begins. However, if the egg is fertilized the implanted embryo produces another hormone called Human Chorionic Gonadotrophin (HCG) which tells the ovary to continue to produce progesterone. When a woman takes a pregnancy test about two weeks later, the level of HCG is detected to determine if there is a positive pregnancy.

There is a great illustration on the fertilization process on this website:



Home Health UK. (2007). What is Fertilization. Retrieved from:

Mosby’s Dictionary of Medicine, Nursing, & Health Professionals. 7th. Ed. (2006). Mosby Elsevier. St. Louis, MO.


Comments are closed.