Regulation of follicle development and novel approaches to ovarian stimulation for IVF

Current ovarian stimulation regimens for IVF are complex and not without ri sk. Increasing our knowledge of the physiology of follicle development and dominant follicle selection may enable the design of less complex, safer an d cheaper ovarian stimulation regimens for IVF. Decremental serum FSH conce ntrations during the follicular phase of the menstrual cycle are required f or single dominant follicle selection. Only the most mature follicle will c ontinue its development due to increased sensitivity for stimulation by FSH . FSH stimulation becomes insufficient for less mature follicles and remain ing cohort follicles will therefore go into atresia, The number of days dur ing which FSH is above the threshold for stimulation of follicle developmen t is limited, resulting in a narrow FSH window. More medium sized and large pre-ovulatory follicles and increased oestradiol output can be induced by the administration of small doses of exogenous FSH during the mid- to late follicular phase, preventing the physiological decrease in FSH stimulation. Intervention,vith decremental serum FSH concentrations in combination with gonadotrophin-releasing hormone (GnRH) antagonists to prevent a premature rise in serum LH may induce ongoing growth of multiple follicles sufficient for IVF. The benefits and risks of these minimal hyperstimulation protocol s require further evaluation.