The Three Stages of Labor are the Dilation, Expulsion, and Placental Stages

Fetal hypothalamus and adrenal glands mature

- Increased CRH from fetal hypothalamus - Lead to increased fetal cortisol release - Fetal cortisol begins positive feedback loop with placental CRH - Cortisol increases placental CRH release - Increases cortisol release even more

Expulsion stage

- Lasts from full dilation to delivery of the infant, or actual childbirth - Crowning occurs when the largest dimension of the baby's head distends the vulva - Episiotomy: Reduce tissue tearing-- incision made to widen the vaginal orifice - Head-first presentation also allows the baby to be suctioned free of mucus and to breathe even before it has completely exited from the birth canal

Major function of progesterone

- Suppress contraction of uterine smooth muscle as it is stretched by the growing fetus - Important for preventing preterm labor

Dilation stage

- Time from labor's onset until the cervix is fully dilated by the baby's head - Contractions become more vigorous and rapid - As the infant's head is forced against the cervix with each contraction, the cervix softens and thins and dilates - Engagement occurs when the infant's head enters the true pelvis

Placental stage

- Delivery of the placenta and its attached fetal membranes

Increase in estrogen

- *Prepares cervix for dilation* - Prostaglandins play a major roe in the thinning and softening of the cervix just before and during labor - *Prepares myometrium of the uterus for contraction* - As the onset of labor nears, gap junctions are formed between myometrial cells to tie them together electrically - *Increases the sensitivity of the myometrium to chemical messengers that cause it to contract* - Rising estrogen action and decreasing progesterone action-- the myometrial cells make abundant receptors for oxytocin