Prolactin, which a woman begins to produce during pregnancy, is the main hormone responsible for breastmilk production from the time the baby is born. Nipple stimulation (such as by baby suckling or breast pump) promotes increased levels of prolactin, especially in the first few months postpartum. Oxytocin, another hormone released in response to nipple stimulation, triggers the “let-down” reflex, the release of milk within the breasts.
Breastmilk production follows a “supply and demand” pattern. Milk flow promotes breastmilk production, while full breasts send the message to decrease breastmilk production. After the first two months, this feedback mechanism becomes the main regulator of milk supply.
These mechanisms allow babies to direct the volume of breastmilk production to match their nutritional needs.
The hormones associated with breastfeeding, including high levels of prolactin, tend to suppress ovulation and menstruation. The length of time that this effect persists varies from woman to woman, and many women experience a return of ovulation and menstruation while still breastfeeding or expressing breastmilk. The timing of the return of a woman’s menstrual cycle while breastfeeding may vary from one birth to the next.
Often, a woman knows that her cycles have returned only after she first ovulates, when she gets her first postpartum period. Some breastfeeding women notice signs of ovulation, such as a drop in milk supply, increased nipple tenderness, or a change in vaginal discharge, while others don’t.
