Chances of Pregnancy - 20-25% for healthy couples - 30-50% conceptions lost by resorption into the uterine wall within the first 6 weeks after conception - 9% lost by miscarriage in first 20 weeks of pregnancy - Causes: - Defect in fetus - Material infection - Structural abnormalities of uterus - Endocrine or immunological disturbances Menstrual cycle - First half: follicular phase - Estrogen stimulates hypothalamus to secrete GnRH - GnRH stimulates pituitary gland to release FSH and LH - FSH prompts growth of follicles, stimulates estrogen production within the follicles - LH causes secretion of progesterone which prompt uterine wall to store glycogen and nutrients - Blood levels of FSH and LH are highest prior to ovulation (day 14) and the LH surge causes the release of an ovum from a follicle for ovulation - Second half: luteal phase - After ovulation - Corpus luteum from the original follicle that released the ovum secretes progesterone and estrogen which inhibit production of GNRH