Once the egg cell is released from the ovary of a woman and the sperm cells are released through ejaculation by man, they only have a limited period of time to live. When a sperm cell fuses with the egg cell, fertilization occurs. If no such meeting occurs, the sperm and the egg die, and the couple wanting to have a baby may have to wait for the next fertile period of the woman. Fertilization, then is the process of uniting the egg and the sperm at the right time, which in turn initiates the beginning of pregnancy and the creation of a new life.

A woman usually ovulates or releases an egg about 14 days after the start of her menstrual period, and the egg has about 18 to 24 hours to be fertilized. Sperm cells can stay in the reproductive tract of the woman for approximately three to five days. For fertilization to happen, sexual intercourse should take place within this fertile period of the woman.

The success of fertilization is often dependent on several factors. These include the timing of sexual intercourse and the health condition of each individual involved in the process. Some men may have low counts of sperm cells, which may affect their chances of getting their partner pregnant. There are also women who have reproductive health problems, like endometriosis and ovarian tumors, which may hinder their ability to conceive. Endometriosis is a condition where cells from the uterus abnormally grow in other sites such as the ovary, fallopian tubes, and cervix.

For these couples who find it difficult to conceive after many years of trying, there are some procedures that can help them have a child. These procedures include the intrauterine insemination and the in vitro fertilization methods. In the intrauterine insemination method, the woman is usually given certain medications to promote egg production. Then when she is determined to be fertile, washed sperm cells from the man are introduced into her uterus for fertilization to occur.

For the in vitro fertilization method, the woman is also given a medication to induce production of many egg cells. Then her cells will be harvested or retrieved from her reproductive tract and placed in a culture media in the laboratory. Sperms cells are then mixed with the egg cells for fertilization to happen. After about two days, selected number of fertilized eggs are then placed in her uterus.