During a menstrual cycle, the hypothalamus secretes the GnRH hormone, which acts on the pituitary gland. The pituitary gland then, release follicle-stimulating hormone (FSH) and lutenizing hormone (LH), also known as Anterior Pituitary Gonadotropins. The secretion of FSH hormone causes 8 to 12 ovarian follicles to develop. On the 8th day of the cycle, one of the eggs will become dominant and, under the influence of LH, will reach ovulation after 4 to 5 days. The rest of the follicles will fail to mature; they will degenerate and will become "atretic". The administered medication aims to rescue these follicles from atresia and help them mature. The administered drugs are synthetic hormones, identical to those released by the female pituitary gland into the brain. The ovarian stimulation is closely monitored by measuring the hormone produced by the maturing follicles and by ultrasound.