Figure 3.

Hormone levels during and after human pregnancy. Estrogen, progesterone and prolactin steadily increase throughout pregnancy. Childbirth is characterized by a rapid drop in estrogen and progesterone and a surge in oxytocin levels that initiates uterine contractions. During breastfeeding in the postpartum period, pulses of prolactin levels stimulate milk production between feedings, alternating with oxytocin pulses, which lead to milk ejection during breastfeeding in response to the infant’s suckling (let-down reflex).