Association between the proportion of dominant follicles and oocyte developmental competence

Purpose To explore the optimal timing for hCG triggering by investigating the impact of different proportion of dominant follicles on the oocyte developmental competence. Methods One hundred ninety-eight infertile women were divided into three groups according to the proportion of dominant follicles on hCG day: (1) low: <15%(n=66); (2) middle: 15-27 % (n=66); (3) high: >27 % (n=66). The grouping criteria were the bottom and top tertiles of the proportion of dominant follicles. Results The gonadotropin dosage, duration and maximum follicle diameter in the low proportion group were lower than those in the middle and high proportion groups. Oocyte maturation and the abnormal fertilization rate in the low proportion group were lower than those in the middle and high proportion groups. The normal fertilization rate did not differ among the three groups. The cleavage rate and number of transferable embryos in the low proportion group were significantly higher than those in the high proportion group. The high-quality embryo rate, implantation rate, and pregnancy rate in the low proportion group were significantly higher than those in the middle and high proportion groups. Conclusions A high proportion of dominant follicles are closely associated with impaired oocyte developmental competence and low pregnancy rate. These findings suggest that follicular overgrowth induced by delayed hCG triggering may undermine oocyte developmental competence and the proportion of dominant follicles may be a potential parameters for hCG triggering.