Incubation with sperm enhances in vitro maturation of the oocyte from the germinal vesicle to the M2 stage.

Objective: To evaluate the effect of sperm in the culture medium on the rate of oocyte maturation in vitro from the germinal vesicle to the M2 stage.

Design: Prospective randomized controlled study.

Setting: The IVF Unit, Wolfson Medical Center, Holon, Israel.

Patient(s): All women in whom oocytes were retrieved at the germinal vesicle stage between December 1995 and March 1996.

Intervention(s): Oocytes retrieved at the germinal vesicle stage were divided prospectively and randomly into four groups of incubation conditions: group 1, intact germinal vesicle with cumulus; group 2, intact germinal vesicle with sperm cells in the culture medium; group 3, stripped germinal vesicle; and group 4, stripped germinal vesicle with sperm cells. Oocytes were observed 24 hours after retrieval, and the stage of maturation was recorded. Oocytes that reached the M2 stage underwent the intracytoplasmic injection procedure, and the fertilization rate in each group was recorded at 48 hours.

Main Outcome Measure(s): Maturation rate from the germinal vesicle to M2 stage and fertilization rate.

Result(s): Each group contained 20 germinal vesicle oocytes. In groups 1 and 2, 2 (10%) and 9 (45%) oocytes, respectively, reached the M2 stage at 24 hours; at 48 hours, 1 (5%) and 8 (40%) embryos developed, respectively. The results in group 2 were significantly higher than in group 1. In groups 3 and 4, 6 (30%) and 16 (80%) oocytes, respectively, reached the M2 stage at 24 hours; at 48 hours, 5 (25%) and 14 (70%) embryos developed, respectively. Results in group 4 were significantly higher than those in groups 1, 2, and 3.

Conclusion(s): Both methods of oocyte activation (i.e., addition of sperm to the culture medium or removal of the cumulus) enhance oocyte maturation in vitro, but the sperm-incubation method has a more pronounced effect. A combination of both methods leads to an exceptionally high rate of oocyte maturation, followed by a high fertilization rate.