Oocyte or egg retrieval is a procedure that marks the beginning of the second phase of an IVF cycle. It occurs when ovarian stimulation with fertility drugs is successfully completed. More specifically, 35 to 36 hours after hCG is administered to trigger the final stages of oocyte maturation and ovulation, a gynecologists under transvaginal ultrasound guidance using a needle punctures and aspirates the follicles.
The fluid containing the oocyte is aspirated into multiple tubes which are then passed to the embryologists, who empties the fluid into a Petri dish and looks for the egg, under the microscope. When the oocyte is located is removed from the mixture of follicular fluid and blood and is placed into a culture medium of specific chemical composition and proper temperature.
Egg retrieval is a relatively easy procedure that takes about 20 to 30 minutes, based on the number of follicles present at the ovaries. The whole process is performed under mild sedation with a recovery period of approximately an hour. However, it is important to notice that for safety reasons, women scheduled for egg retrieval must be at the clinic at least 30 minutes before the procedure in order to have a cardiograph and talk to the anesthesiologist about allergies, any medication they are taking and any other health problems they may have. Last but not least, women programmed for this procedure shouldn’t eat or drink anything from the previous night.
Sperm collection and preparation
On the day of egg collection, the husband gives a sperm sample. The semen specimen should be obtained following a 3-4 day abstinence from sexual activity and masturbation is the preferred method of collection. A shorter or longer period of time or the use of a different method of collection (lubricants, silastic condoms) may affect semen parameters. After collection the semen sample is delivered to the lab where it is properly prepared for IVF. The purpose of the preparation is to isolate the motile spermatozoa from other elements of the semen and activate them in order to be capable to fertilize the mature oocytes.
It should be noticed that masturbation, especially at the clinic, is sometimes difficult and stressful for men on the day of egg collection. Therefore men could bring the semen sample from home or can freeze a sample several days before the day of oocyte retrieval (fresh samples are always preferred). In cases of men with azoospermia, spermatozoa are retrieved directly from the testis (surgical sperm retrieval).
Oocyte Fertilization
Several hours after egg retrieval and semen preparation, fertilization occurs. More specifically at a conventional IVF cycle the mature oocytes are placed in 4-well dishes of culture medium containing processed sperm. One of the spermatozoa will penetrate and fertilize the oocyte. In cases of severe male infertility, other laboratory techniques are required following egg retrieval. Fertilization may be assisted by intracytoplasmic sperm injection (ICSI) , a micromanipulation technique which involves the injection of a sperm directly into the egg. The eggs are then incubated in the lab overnight.
The next morning, 16-18 hours after the time of fertilization, fertilization check is performed by the embryologists. The first signs of normal fertilization are shown by the presence of two pronuclei (small round structures) within the egg. The fertilization rate is usually between 50 and 100%. The maturity of the oocytes, semen parameters, handling procedures and culture systems are some factors that are responsible for the variance in the fertilization rate .
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