There are several ways fertilization can occur:

  • The natural way, via sexual intercourse between a man and a woman
  • Intrauterine Insemination, also known as IUI, which is done in a doctor’s office by transferring sperm directly into the uterus via a catheter
  • In vitro fertilization, which is far more complicated and done manually at an infertility clinic.

This article will describe, in general, these three methods of fertilization.

Fertilization the Natural Way

With sexual intercourse, Intrauterine Insemination and IVF, in order for the egg to be fertilized, the head of the sperm attaches to the egg. As they merge together the obvious membranes take all the contents of the sperm into the egg, which causes the egg to immediately release a fluid called cytosol.Cytosol doesn’t allow other sperm in once they finally “arrive on scene.”

The nucleus of the male increases in size to form the male pronucleus, while the egg enlarges to form the female pronucleus. The two nuclei then begin to form a set of chromosomes. Once this happens, fertilization has occurred and implantation is set to take place.

With sexual intercourse and Intrauterine Insemination,  the woman’s body is then alerted that it’s time for preparation and production of hormones to move the process along.

Fertilization via Intrauterine Insemination

In the case of Intrauterine Insemination also known as IUI, the mother usually is given medication to stimulate multiple egg development and the insemination is timed to coincide with ovulation.

Once this has been established a speculum is placed in the vagina and the cervical area is gently cleaned. Then the separated and washed specimen consisting of a purified fraction of highly motile sperm is placed either in the cervix (intra cervical insemination) or higher in to the uterine cavity (intrauterine insemination, IUI) using a sterile, thin and soft catheter.

Intrauterine insemination has a better success rate than intra cervical insemination—as indicated above, fertilization takes place the same way it would if the woman became pregnant during sexual intercourse. Therefore, it is the preferred method at most fertility clinics.

Fertilization via In Vitro Fertilization

In vitro fertilization, also known as IVF, takes place in a laboratory within the infertility clinic. After much medication and monitoring, the reproductive endocrinologist retrieves the eggs from the mother or egg donor and the embryologist oversees the fertilization process. IVF is the process of generating human life when other methods have failed. The eggs (also referred to as ova) and sperm are mixed together until the viable eggs are fertilized and embryos are developed. Once fertilization has occurred, usually no more than two embryos are then transferred back into the mother or gestational carrier in hopes that at least one embryo will implant itself in the lining of the uterus. IVF should be monitored closely by the doctor involved to ensure the safety of both the mother and the baby. At approximately 10–12 weeks, the pregnant woman is then released from the infertility clinic to the OB of her choice, and the pregnancy is treated like a normal occurrence.

[Page updated November 2015]