[Oocyte fertilizability and hormonal environment of human preovulatory follicles in hyperstimulated cycles in an in vitro fertilization program: Are mature preovulatory follicles undergoing atresia?].

Steroid hormones in preovulatory follicular fluid, maturity of the oocyte-corona-cumulus complex (OCCC), and oocyte fertilizability were studied in 55 hyperstimulated cycles in 40 patients who were indicated for in vitro fertilization and embryo transfer due to tubal infertility. Aspirated follicles were categorized into four groups according to the degree of oocyte maturation and fertilizability, i.e. follicle (Fol)-1 (non-fertilized, intermediate maturation), Fol-2 (fertilized, intermediate maturation), Fol-3 (fertilized, full maturation), and Fol-4 (non-fertilized, full maturation). Estradiol (E2), progesterone (P), and delta 4- androstenedione (delta 4A) concentrations were highest in Fol-3, being lower in Fol-2 and Fol-1 sequentially. Fol-3 contained significantly more E2 and P than did Fol-1, showing that the degree of oocyte maturation and fertilizability correlate with concentrations of E2 and P in the follicles. A comparison of Fol-3 and Fol-4 revealed significantly higher concentrations of delta 4A in Fol-4, whereas differences in E2 and P concentrations were not significant although Fol-4 values were lower. This comparison indicated that Fol-4 were already undergoing atresia at the time of oocyte retrieval, containing morphologically mature OCCC which had lost fertilizability. This study shows that steroid hormones in the follicular fluid reflect oocyte viability and fertilizability, and suggests that preovulatory follicles with mature oocytes can also undergo atresia.