A prolactin test measures the level of prolactin, which is made by the pituitary gland, in your blood. Pregnant women have high levels of prolactin, which aids in making breast milk. During pregnancy, prolactin levels will increase by 10 to 20 times. After the infant is born, prolactin stays high if you are breast-feeding. In those who do not breast-feed, prolactin levels return to normal soon after they give birth. Prolactin levels may also return to normal levels even if you still breast-feed after months of breast-feeding.
The pituitary glands of men and nonpregnant women make prolactin as well but it is not clear what it does in the body for these people.
Prolactin levels change throughout the day. The highest levels occur during sleep and shortly after waking. Prolactin levels are also higher during times of physical or emotional stress.
