Follicular fluid nitric oxide (NO) concentrations in stimulated cycles: the relationship to embryo grading

The microenvironment of the ovarian follicle is vital for normal oocyte development, folliculogenesis, and timely ovulation. We investigated the concentration of nitric oxide (NO) in follicular fluid, collected during oocyte retrieval after in-vitro fertilization and embryo transfer (IVF-ET) and its relationship to oocyte and embryo grading.

A total of 53 follicular fluid samples were obtained from 15 patients undergoing IVF-ET program, oocyte retrieval by transvaginal guidance was per formed approximately 34-35 h after the hCG administration in stimulated cycles. Using a modified grading system the samples were divided in Group 1 with very few fragments in the cytoplasm with equal size blastomeres (best embryos) and Group 2 with significant or severe fragmentation or blastomeres of distinctively unequal size. Follicular NO was measured as nitrite/nitrate.

The mean concentration of NO follicular fluid is significantly higher in Group 2 than in Group 1 (57.54 +/- 12.67 nmol/mg vs. 42.43 +/- 16.32 nmol/mg). Using the correlation analysis, we observed a direct correlation between follicular NO and embryo grading (r = 0.61; P < 0.001) and an inverse correlation between follicular NO and serum 17beta-estradiol (r = -0.28; P < 0.05).

High levels of NO in human follicles may be detrimental. The inverse correlation found between NO and serum concentrations of 17beta-estradiol may be explained as a regulation of estradiol on maturation process of the oocytes and embryos in stimulated cycles through NO mediation.