What physiological factor explains why a newborn might produce breast milk shortly after birth?

The production of breast milk by a newborn shortly after birth can primarily be attributed to the influence of maternal hormones. During the later stages of pregnancy, maternal hormones, particularly estrogen and progesterone, prepare the breast tissue for lactation. After the birth of the baby and the expulsion of the placenta, there is a sudden drop in these hormones, which allows for the rise of prolactin levels. Prolactin stimulates the mammary glands to begin milk production, which is often observed as a small amount of substance that may resemble milk or colostrum being expressed or found in the newborn's mouth.

While enzymatic changes in the infant's gut are important for digestion and absorption, they do not directly lead to milk production by the newborn. Newborns do not naturally produce milk; rather, they initiate feeding behaviors that stimulate the mother's milk production. The transfer of colostrum from the mother to the baby is vital for the newborn's early nutrition but does not account for the production of milk by the infant itself. Hence, the correct reasoning lies in understanding how maternal hormones impact the newborn's ability to produce milk shortly after delivery.