Fertilization

The IVF laboratory starts preparing for your eggs the day before the retrieval by setting up the culture dish where fertilization will happen. Immediately after the retrieval, an embryologist looks at the material retrieved, finds the eggs, and inseminates them either by adding sperm to the dish or by performing intracytoplasmic sperm injection (ICSI). ICSI is used for sperm that are unable to fertilize an egg on their own. In this technique, a technician uses a powerful microscope with a very tiny needle to inject a single sperm into an egg. At some clinics, fully half of the IVF cycles are done using ICSI.

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The embryos are cultured in a very special lab. Everything that touches a human embryo has to go through an extensive process of testing and cleaning. Everything from the culture dishes to the countertops (heated to body temperature) to the floor (sticky, to hold dust) are specially designed for human embryo culture. Patients don't need to visit the lab; between egg retrieval and embryo transfer, the process goes on without you.

Sixteen to 20 hours after insemination, the embryologist checks for fertilization, setting aside any eggs that did not fertilize normally. The lab can then update you on how many eggs fertilized. The embryos are left to divide until day three, when they should have six to eight cells each.

On day three, the embryologist grades the embryos based on the number of cells and how well they appear to be developing. The embryos are usually transferred to the uterus on day three, but in some cases they may be cultured longer. Culturing the embryos until day five--when embryos should have formed into a hollow ball known as a blastocyst--lets the embryologist get a better sense of how healthy they are. This gives couples the opportunity to improve their chances of a pregnancy without the risk of a high order multiple gestation.

In some cases, the lab may perform assisted hatching, which means it makes a tiny hole in the zona pellucida, the shell that surrounds and protects the embryo. When the embryo implants, it has to break through the zona pellucida; assisted hatching may help the embryo get out of the shell.

Most embryologists are not medical doctors, but have a background in biology with several years of education in embryology (the study of embryos and how they develop). Most have certification in embryology and andrology from the American Association of Bioanalysts.