From the Guidelines
Prolactin levels increase during pregnancy primarily due to the stimulation of the pituitary gland by rising estrogen levels produced by the placenta. As pregnancy progresses, estrogen stimulates the pituitary gland to produce more prolactin, with levels increasing significantly. This increase is essential for preparing the mammary glands for milk production after childbirth. The evidence from 1 suggests that prolactin remains elevated in breastfeeding women, and breastfeeding bouts trigger acute increases in both prolactin and oxytocin. Some key points to consider include:
- The placenta itself produces prolactin-like hormones, which contributes to the overall prolactin effect
- The pituitary gland enlarges during pregnancy, allowing for greater prolactin production
- Progesterone works alongside prolactin to develop milk-producing cells in the breasts, though it temporarily blocks milk production until after delivery
- Prolactin levels remain elevated to maintain milk production, especially in response to the baby's suckling, as seen in breastfeeding women 1. The interplay between these hormones ensures that the mother's body is prepared for lactation once the baby is born. In the context of real-life clinical medicine, understanding the physiological changes during pregnancy, including the increase in prolactin levels, is crucial for managing pregnancy-related complications and supporting lactation in new mothers.
From the Research
Causes of Increased Prolactin Levels During Pregnancy
- Prolactin levels rise rapidly during pregnancy due to an increase in the size and number of lactotrophs in the anterior pituitary gland 2
- The main function of prolactin is during pregnancy and lactation, where it plays a crucial role in the development of mammary glands, milk synthesis, and maintenance of milk secretion 2, 3
- The increase in prolactin secretion during pregnancy is physiological and necessary for lactation 4, 5
- Elevated levels of progesterone during pregnancy prevent prolactin from exerting its effect on milk secretion, but after parturition, the decrease in progesterone levels allows prolactin to stimulate milk production 3, 5
- Prolactin levels decrease as lactation is established, but nursing stimulates prolactin release from the pituitary, promoting continued milk production 3
Physiological Changes During Pregnancy
- The concentration of circulating prolactin increases during pregnancy, reaching levels 10 to 20 times higher than normal by the end of gestation 3
- The pattern of prolactin heterogeneity changes during pregnancy, favoring more monomer in proportion to the dimer 3
- Prolactin is secreted into milk at levels representative of the average circulating concentration, but its physiological significance to the infant is uncertain 3
Clinical Implications
- Hyperprolactinemia during pregnancy can be physiological or pathological, and serial prolactin measurements are essential in monitoring patients with prolactinomas 6
- Maternal hyperprolactinemia or failure of prolactin to increase during pregnancy do not influence the secretion of placental hormones or prolactin concentration in amniotic fluid and the newborn 6