Egg Fertilization

In-vitro fertilization is based on a simple principle: if eggs are obtained and fertilized in the laboratory, most will produce embryos, and some of these will be healthy and will very often produce a pregnancy if placed in the uterus during the third to fifth day of life. Obtaining the eggs requires a sequence of medications that result in the maturation of many eggs at once, which can be retrieved with an ultrasound guided needle under light anesthesia. Fresh sperm are used to fertilize the eggs the same day. The resulting fertilized eggs are maintained in sophisticated and carefully controlled laboratory conditions while they undergo repeated cell divisions. After a few days, a some of these will be clearly the healthiest, and generally two are returned to the uterus in a simple procedure using a fine catheter.

Egg being fertilized


Normally two embryos are placed to increase the chance of pregnancy overall, but this practice comes at a cost of producing twins in about one-third of resulting pregnancies. Sometimes one pregnancy will fade away while the other succeeds so that only a single baby arrives at term. Sometimes both embryos will succeed, and one will split so that triplets will occur. This will happen in about one of fifty in-vitro fertilization pregnancies in the center. The center rarely places more than two embryos, and sometimes only one is placed. It is important to reduce the incidence of triplets as much as possible as these pregnancies are often high risk for the mother and babies and can result in babies with lasting handicaps. Placing too many embryos can do more harm than good. The decision about how many embryos to place is always determined between physician and couple after careful discussion at the time of the embryo transfer.


In-vitro fertilization is equally effective for almost all infertility conditions. Pregnancy is detectable after two weeks, and close to three quarters of women undergoing this procedure will have a positive pregnancy test. Some of these pregnancies will fade after a few days, but most will persist and thrive. Pregnancy rates in successful clinics, such as the Utah Center for Reproductive Medicine, will exceed 50% per try. The success rate is dependent on a woman’s age with rates of pregnancy slightly lower after 35 and much lower after 40.

Infographic about IVF