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The Ins and Outs of In Vitro Fertilization (IVF)

Eggs Meet Sperm

After the eggs are retrieved, they are handed over to the embryology lab, where they are placed in small dishes or tubes containing "culture medium." This special fluid is designed to resemble the environment in the fallopian tube or uterus. These dishes are then placed into incubators, where the temperature and atmospheric gases can be controlled.
A few hours after the egg retrieval, sperm are placed in the culture medium with the eggs. In some cases, couples may choose a method called intracytoplasmic sperm injection (ICSI). This method involves using special micromanipulation equipment (joystick-controlled robotics) and individually injecting a single sperm into the cytoplasm (interior) of each mature egg. ICSI can be especially effective for severe male factor infertility. The injected eggs are returned to the laboratory incubator and treated the same as the eggs that would not have undergone the ICSI procedure.

Incubating and Waiting

Once the eggs are mixed with the sperm, they are returned to the incubator -- and the waiting begins. Over the next few days, the dishes are inspected and the development of the embryos is assessed.
The day after the eggs are inseminated, they are examined for signs that fertilization has occurred. It's important to understand that although the eggs are mixed with the sperm, or even injected with a sperm, it does not mean that fertilization will be successful. If an egg has been fertilized, normal development on this first day after insemination still involves the single cell that has two nuclei -- this stage is called a zygote.
Two days after insemination, normal embryos will have divided into about four cells. Three days after insemination, embryos should have about eight cells. Five days after insemination, the embryos reach the blastocyst stage, which is when 80 or more cells are present. A blastocyst will also have an inner fluid-filled cavity and a small cluster of cells called the inner cell mass.
Because many eggs and embryos are abnormal, not all eggs will fertilize and not all embryos will divide at a normal rate. The rate of success that a developing embryo will result in a pregnancy is related to how "normal" its development is in the laboratory setting.
However, this correlation is not perfect. Although some embryos develop normally, it does not mean that they are genetically normal. Also, if an embryo develops poorly, it does not mean it is genetically abnormal. However, the visual appearance and development is the most commonly used guide to help in the selection of which embryos will be transferred back into the uterus.
In some cases, people may choose to perform a preimplantation genetic diagnosis (PGD) and a preimplantation genetic screening (PGS). These procedures are used to test embryos for genetic disorders before they are transferred into the uterus. These techniques may be beneficial for couples who have serious inherited disorders. By using PGD and PGS, it is possible to help decrease the risk of having a child who would be affected by the same problem.
These procedures involve the use of a micromanipulator to remove a cell from an embryo. The cell can be examined through diagnostic testing to determine whether the genes that carry certain diseases are present in the embryo. These procedures can help to rule out any genetic disorder or chromosomal disorder, allowing for only the "normal" embryos to be transferred into the uterus.
Last reviewed by: Arthur Schoenstadt, MD
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