Menstrual cycle
Usually, the amount of FSH in the body peaks during the third or fourth day of menstruation.  All but one of the follicles dies off.  The one that is left releases even more estrogen.  Once again, the lining of the uterus thickens.  Near the end of the stage, a woman's estrogen levels peak.  This causes the pituitary gland to release LH, which also peaks at this time.