Ontwikkeling en selectie van follikels als voorwaarde voor vrouwelijke vruchtbaarheid

The development of the pre-ovulatory follicle takes at least 85 days. It is a randomly initiated process regulated independently of stimulation by gonadotropins. The final phase however is dependent on FSH which rises during the luteo-follicular transition of the normal menstrual cycle. The magnitude and duration of this rise influences the number of follicles (normally one) which will develop to the pre-ovulatory stage rather than undergo atresia. Studies indicate that there is a large inter-individual variation in follicular phase FSH levels in normo-ovulatory women. This may reflect individual variation in the modification of the FSH signal by intra-ovarian factors such as insulin-like growth factors and inhibin. Following ovulation, the empty follicle undergoes luteinization and switches to primarily progesterone production. In the absence of pregnancy, the corpus luteum ceases to function and sex steroid levels fall. The reduced negative feedback at the hypothalamus results in a rise in FSH thus enabling the next cohort of follicles to enter the final phase of maturation.