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Chapter 22 Lactation
Jennifer Deirmengian, MD
❍ When do prolactin levels peak in pregnancy and postpartum?
Prolactin levels peak at the time of delivery. The normal range varies, but in one study the mean value at term
was 207 ng/mL. Baseline prolactin levels slowly decline after delivery, with levels of 35 ng/mL after 6 months
postpartum. Prolactin levels increase by 80% to 150% with nipple stimulation.
❍ Why does lactogenesis, or actual lactation, not occur during pregnancy even though the prolactin levels
are elevated?
The receptor sites in the breast are competitively bound by estrogen and progesterone, preventing prolactin from
activating lactation. When the placenta is delivered, these levels of estrogen and progesterone rapidly drop and the
prolactin floods the receptors.
❍ Suckling produces a pulsatile release of what substance and where does it originate?
Oxytocin, from the posterior pituitary.
❍ What is the letdown reflex?
The letdown reflex describes the secretion of oxytocin in response to infant suckling or maternal clues related to
nursing. The oxytocin causes myoepithelial cells in the breast to contract, resulting in ejection of milk.
❍ Does oxytocin have any other physiologic effects?
Yes. It causes uterine contractions in the immediate postpartum period. This is thought to aid in uterine
involution.
❍ What is the area of the breast that stores milk in preparation for the infant to extract? Where is this located?
What is the clinical significance?
The lactiferous sinuses are located just behind the areola. The lactiferous ducts, which drain from the alveolar sacs,
empty into the sinuses. If the infant is not positioned such that his/her mouth is over the areola, the infant will
suck only on the nipple and have to frequently regrasp the breast to suckle. This results in sore nipples and fissures,
leading to possible mastitis.