Increased serum prolactin during pregnancy causes enlargement of the mammary glands of the breasts and increases the production of milk.
Sometimes, newborn babies (males as well as females) secrete a milky substance from their nipples. This substance is called Witch's milk. This is caused by the fetus' being affected by prolactin circulating in the mother just before birth, and usually stops soon after birth.
There is a Diurnal as well as a ovulatory cycle variation in prolactin levels. During Pregnancy, prolactin levels rise as rising Estrogen promotes prolactin release, causing further maturing of mammary glands, preparing them for lactation. After Childbirth, prolactin levels fall as the internal stimulus for them is removed. Sucking by the baby on the nipple promotes further prolactin release, maintaining the ability to lactate. Usually, in the absence of Galactorrhea, lactation will cease within one or two weeks of the end of demand Breastfeeding. High prolactin levels also tend to suppress the ovulatory cycle by inhibiting both FSH and GnRH.
As a contraceptive, demand breastfeeding is said to be more than 90% effective in the first month of post-partum even if no other forms of contraception are used, with decreasing effectiveness in successive months. It is not advised, however, that one rely on this method as the only contraceptive for any long period of time.
Hyperprolactinaemia is the term given to having too-high levels of prolactin in the blood. Prolactin levels may be checked as part of a sex hormone workup, as elevated prolactin levels suppress FSH and GnRH and hence lead to Hypogonadism. Prolactin levels may be of some use in distinguishing epileptic seizures from Psychogenic non-epileptic seizures.