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[20] [4] [21] During pregnancy, prolactin increases can range up to 600 ng/mL, depending on estrogen and progesterone concentrations. After delivery, progesterone concentrations decrease, and prolactin levels drop. Only during nipple stimulation will prolactin levels rise, allowing for milk production. [22]
OL is the stage when plentiful production of milk is initiated following the delivery of a full-term infant. [5] [6] It is stimulated by an abrupt withdrawal of progesterone and elevation of prolactin levels after the complete expulsion of placenta. [5] [6] The other two stages of milk production are stage I lactogenesis and stage III ...
Prolactin has a wide variety of effects. It stimulates the mammary glands to produce milk (): increased serum concentrations of prolactin during pregnancy cause enlargement of the mammary glands and prepare for milk production, which normally starts when levels of progesterone fall by the end of pregnancy and a suckling stimulus is present.
High levels of prolactin during pregnancy and breastfeeding also increase insulin resistance, increase growth factor levels (IGF-1) and modify lipid metabolism in preparation for breastfeeding. During lactation, prolactin is the main factor maintaining tight junctions of the ductal epithelium and regulating milk production through osmotic balance.
It will contract midline with the umbilicus. It begins its contractions and by twelve hours after the birth it can be felt to be at the level of the umbilicus. [9] The uterus changes in size from one kilogram to 60-80 grams in the space of six weeks. After birth, the fundus contracts downward into the pelvis one centimeter each day.
During pregnancy, the production of prolactin by the mother increases steadily, starting at 6–8 weeks of gestation and continuing until the end of the pregnancy. [32] Prolactin levels in the human fetal circulation see a gradual increase from around 30 weeks of gestation until birth. [ 32 ]
Estrogen and progesterone cause the secretion of high levels of prolactin from the anterior pituitary, [32] [33] which reach levels as high as 20 times greater than normal menstrual cycle levels. [31] IGF-1 and IGF-2 levels also increase dramatically during pregnancy, due to secretion of placental growth hormone (PGH). [34]
High levels of progesterone, which are associated with pregnancy, inhibits prolactin and therefore lactation. [30] Prolactin increases during the initial stages of lactation and can be stimulated by estrogen but not progesterone. [30] Research, however, focuses on the role of prolactin for breastfeeding and less on other behaviors. [30]