Oocyte Retrieval in Double Stimulation

Abstract

Follicle growth from the resting primordial stage until the pre-ovulatory phase takes several months; only the last 2 weeks of this long trajectory are dependent on gonadotropin support (Fig. 11.1) [1]. If maturing antral follicles achieve a distinct stage of development, they are programmed to die, but if serum FSH levels surpass a threshold, these follicles are rescued from atresia, i.e., gain gonadotropin dependence and continue their development [2]. Under normal conditions, elevated FSH levels above the threshold occur during the luteo-follicular transition. The subsequently follicular estradiol secretion inhibits pituitary secretion of FSH, which in turn causes the FSH concentration in the developing cohort follicles to drop below the threshold, the decreased FSH concentrations during the follicular phase are crucial for single dominant follicle selection (Fig. 11.2) [2]. The number of follicles recruited can be increased if endogenous FSH levels are augmented by exogenous gonadotropins or can be reduced if FSH levels are sufficiently diminished [3].