when do mammary glands produce milk during pregnancy
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:
Breastfeeding Changes early in pregnancy prepare the breast for lactation. Pre-birth hormone levels become altered after the birth and stimulate the production of milk. From around halfway through pregnancy, the breasts begin to produce colostrum.[17] Colostrum, a thick yellowish fluid rich in protein, continues to be produced for the first few days after delivery. Around 30 to 40 hours after delivery, the composition of milk changes to mature milk and milk volume becomes copious, an event known as the milk "coming in".[18] Sucking causes the pituitary to release oxytocin that causes to the contraction of the uterus.[19][20] Progesterone is the hormone that influences the growth of breast tissue before the birth. The postpartum changes that occur in the endocrine system after the birth shift from hormones that prevent lactation to hormones that trigger milk production.[citation needed] This can be felt by the mother in the breasts. The crying of the infant can induce the release of oxytocin from the pituitary gland.[21]
Breastfeeding Changes early in pregnancy prepare the breast for lactation. Before pregnancy the breast is largely composed of adipose (fat) tissue but under the influence of the hormones estrogen, progesterone, prolactin, and other hormones, the breasts prepare for production of milk for the baby. There is an increase in blood flow to the breasts. Pigmentation of the nipples and areola also increases. Size increases as well, but breast size is not related to the amount of milk that the mother will be able to produce after the baby is born. By the second trimester of pregnancy colostrum, a thick yellowish fluid, begins to be produced in the alveoli and continues to be produced for the first few days until the milk "comes in", around 30 to 40 hours after delivery.[17] [18] Oxytocin contracts the smooth muscle of the uterus during birth and following delivery, called the postpartum period, while breastfeeding. Oxytocin also contracts the smooth muscle layer of band-like cells surrounding the alveoli to squeeze the newly produced milk into the duct system. Oxytocin is necessary for the milk ejection reflex, or let-down, in response to suckling, to occur.[19]
Embryo In humans, a pregnancy is generally considered to be in the embryonic stage of development between the fifth and the eleventh weeks after fertilization,[1] and is expressed as a fetus from the twelfth week.