Once the follicles have grown and eggs matured, the eggs (oocytes) are retrieved from patients by transvaginal aspiration directly from the ovarian follicles, a process called Oocyte Pick-Up (OPU) or "egg retrieval ". This occurs approximately 36 hours after the trigger injection. An embryologist will examine the collected follicular fluid to identify and collect the eggs.
The dishes containing the collected eggs in insemination culture media are placed in an incubator, with tightly controlled environmental conditions (light, oxygen and carbon dioxide concentrations, pH, and temperature). The oocytes are left for a few hours to complete their maturation. The day of the oocyte retrieval is referred to as “Day zero” of embryo culture.