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IVF Process: Fertilization and Embryo Development

Step four: Fertilization

Prior to embryo development, fertilization must first occur. Once the eggs and sperm are collected, sorted, and prepared, Shady Grove Fertility’s specially trained embryology team begins the fertilization process. There are two methods used for fertilization:

Conventional fertilization
Conventional fertilization is a standard form of fertilization used during the IVF process and frequently used in cases such as blocked Fallopian tubes or unexplained infertility. The embryologist starts by “washing the semen” allowing him/her to isolate the healthy sperm, which are then placed around each egg so fertilization can occur.

Intracytoplasmic sperm injection (ICSI)
ICSI is used in cases when the quantity or quality of sperm is poor and therefore unable to effectively penetrate the egg on its own. The embryologist selects a single sperm and injects it directly into the center of each egg. Since fertilization only requires one healthy sperm, ICSI has become one of the most incredible advancements in treating severe male factor infertility.

The decision about which method to use is based on the quality of the sperm. To test sperm, a semen analysis is completed as part of the initial basic fertility work-up for diagnosis before treatment and then again when the semen sample is provided on the day of the egg retrieval. If the results from this analysis do not meet the parameters required for conventional fertilization, the embryologist will make the decision to switch to ICSI so that the cycle can still produce embryos and increase your chances of success. The clinical team will let you know if an unplanned ICSI procedure is recommended.

Embryo development

Embryo development begins when the fertilized eggs are placed in an incubator overnight. Then, every morning for the following 3 to 5 days, an embryologist examines each patient’s developing embryos. The embryologist make notes about what has occurred since the previous day and adds them into the patient’s electronic record.

The goal is to see the slow and steady development of a 4-cell embryo on the second day of development into an 8-cell embryo on the third day. After the 8-cell stage, cell lines begin to blur and the embryo enters what is called the blastocyst stage at day 5 or 6. The blastocyst has a protective jelly-like shell called a zona pellucida and defined areas of cells within it. The organization of what is called “the inner cell mass” is a key indicator of how likely the embryo is to implant.

Step 5: Embryo Transfer

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