Hormones of Lactation
From the eighteenth week of pregnancy (the second and third trimesters), a woman's body produces hormones that stimulate the growth of the milk duct system in the breasts:
➤ Progesterone inhibits lactation before birth but then levels drop after birth allowing for milk production.
➤ Estrogen stimulates the milk duct system to grow and differentiate. High levels of estrogen reduce or stop lactation which is why breastfeeding mothers should not take estrogen-based birth control.
➤ Prolactin stimulates growth of the alveoli, and also influences differentiation of ductal structures.
➤ Human placental lactogen (HPL) is produced in the 2nd month of pregnancy and stimulates breast, nipple, and areola growth before birth.
➤ Follicle stimulating hormone (FSH), luteinizing hormone (LH), and human chorionic gonadotropin (hCG), through control of estrogen and progesterone production, are important hormones for keeping the fertilized egg secure in the uterus.
➤ Growth hormone (GH) contributes to galactopoiesis.
➤ Adrenocorticotropic hormone (ACTH) and glucocorticoids help to stimulate lactation.
➤ Thyroid-stimulating hormone (TSH) and thyrotropin-releasing hormone (TRH) are galactopoietic.
➤ Oxytocin stimulates milk ejection reflex, or let-down, in response to suckling.