Mapping the Nitric Oxide Axis in IVF: Genotype Associations in Antagonist Cycles.

Endothelial nitric oxide synthase (eNOS, NOS3) regulates steroidogenesis, redox signalling, and the vascular tone of the ovaries. Despite varying outcomes in previous studies, the prevalent NOS3 rs1799983 (Glu298Asp) polymorphism may influence endocrine function during controlled ovarian stimulation (COS). On the retrieval day, we assessed follicular-fluid hormones, day-3 hormones, and controlled ovarian stimulation (COS) outcomes (follicles, oocytes, MII oocytes, embryos) in 62 antagonist IVF/ICSI cycles classified by NOS3 genotype (GG/GT/TT). The outcomes for COS and early-cycle hormones were mostly consistent across all genotypes. A similar allele-dose pattern was seen for baseline oestradiol (GG < GT < TT), with heterozygous carriers displaying higher levels of follicular-fluid β-hCG relative to GG individuals. No changes were seen in follicle count, oocyte production, nuclear maturation, or embryo development. Baseline oestradiol and follicular β-hCG serve as the principal indications of the modest, context-dependent endocrine effects of the NOS3 rs1799983 polymorphism in antagonist cycles. To clarify the clinical significance of these intricate genotype-associated patterns, additional comprehensive, genotype-balanced investigations that include direct NO-pathway phenotyping are essential.