Overview Fertilization and implantation ovum is fertilized in ampulla of Fallopian tube several hours after ovulation blastocyst implants in endometrium 6 to 7 days after ovulation syncytiotrophoblast cells secrete hCG that rescues corpus luteum hCG in first trimester,hCG sustains corpus luteum in presence of falling LH levels corpus luteum produces progesterone progresterone is necessary for maintenance of pregnancy hCG levels detectable in blood (1 week post-conception) hCG levels detectable in urine (2 weeks post-conception) e.g., home pregnancy test in second and third trimesters, placenta produces estrogen and progesterone corpus luteum degenerates hCG levels elevated in certain pathologies hydatidiform moles choriocarcinoma Lactation post-delivery, ↓ progesterone levels, prolactin promotes lactation initiation of milk production by alveolar cells Suckling stimulates sensory nerves that carry suckling signal from breast to hypothalamus via spinal cord, a process that mediates prolactin and oxytocin release Prolactin suckling sends signal from breast (nipple) to hypothalamus suckling input in arcuate nucleus of hypothalamus inhibits dopamine release dopamine travels via hypothalamic-portal system to anterior pituitary to inhibit prolactin (PRL) release by lactotrophs suckling inhibits release of dopamine and causes ↑ PRL prolactin promotes lactation and maintains lactation once established prolactin → (-) hypothalamus → ↓ GnRH → ↓ FSH and ↓ LH prolactin inhibits reproductive function Oxytocin suckling sends signal from breast (nipple) to hypothalamus suckling input in supraoptic and paraventricular nuclei of hypothalamus triggers oxytocin release via posterior pituitary oxytocin promotes contraction of myoepithelial cells → promotes milk letdown oxytocin may promote uterine contractions in childbirth Relaxin leads to sacroiliac joint laxity and widening of the pubic symphysis in preparation for delivery Physiologic changes increased red blood cell mass increased plasma volume increased cardiac output decreased vascular resistance mild respiratory alkalosis due to increased tidal volume hypercoagulability increased glomerular filtration rate supine positioning can result in hypotension due to compression of the IVC by the gravid uterus