Optimization of hydrogen-ion concentration during aspiration of oocytes and culture and transfer of embryos.

Rapid and marked shifts in pH can have deleterious effects on oocytes and embryos. Such shifts are most likely to occur during laparoscopy and examination of gametes and embryos. We studied the rate of pH change of follicular fluid and bicarbonate- and phosphate-based media during exposure to 100% CO2 with a constant surface area to volume ratio. All solutions tested developed a pH below the physiological range of 7.30-7.50 within 2 min of exposure to 100% CO2. We also examined the rate of increase in pH due to CO2 loss from media in room air within standard organ culture dishes and tubes. After exposure to ambient conditions for 2 min, the pH of modified Ham's F-10 medium in organ culture dishes rose above the physiological range. We have used a needle laparoscope to confirm intraperitoneal placement prior to the insufflation of a 5% CO2 gas mixture for laparoscopic oocyte retrieval. We have carried out all examinations of oocytes and embryos within a pediatric isolette equipped with an automatic CO2 controller to maintain a 5% CO2 environment. We have transferred embryos in 15% fetal cord serum to avoid the alkaline pH associated with a high concentration of equilibrated heat-inactivated preovulatory serum. These simple techniques can optimize the hydrogen-ion concentration of media during the entire process of in vitro fertilization and embryo transfer.