Throughout the period of Controlled Ovarian Hyperstimulation (COH) follicular growth is monitored by ultrasound. Once the leading follicle is at least 16 mm in diameter, an ovulation-inducing

fertility drug is administered. Oocytes are aspirated from follicles immediately before ovulation (between 34 h and 36 h following hCG administration).

Egg retrieval, also called Ovarian Puncture (OPU), is conducted using a long thin needle, attached to a vaginal ultrasound probe, which allows the doctor to guide the needle through the wall of the vagina and into a mature follicle. Once the needle has punctured the follicle, a suction pump connected to the needle is used to suck the egg cell and some of the follicular fluid. While the procedure is repeated for all mature follicles in both ovaries, the collected fluid is examined under the microscope by the embryologist in the adjacent IVF laboratory. The embryologist isolates the oocytes and transfers them into a special liquid called culture medium, so they can be later fertilized in-vitro.

Egg retrieval is usually performed under sedation, which induces light sleep and makes the procedure painless for the patient. She wakes up about 5-10 min after the procedure and is kept in the recovery room for observation for another 1.5-2 hours.