colostrum

Colostrum is the very first milk, the thick, yellowish fluid a breast produces in the first few days after birth. Think of it as a small, concentrated welcome package: little in volume but extraordinarily rich in protective ingredients for a newborn's first taste of food.

It is produced under hormonal control: the breast begins making colostrum late in pregnancy, but its full release is held back by high placental progesterone. After delivery, when progesterone drops, prolactin can drive secretion freely, and colostrum flows. It is dense with antibodies (especially secretory IgA), white cells, growth factors and proteins that protect and prime the infant's gut and immune system.

Over the first days, colostrum gradually transitions to transitional milk and then to mature milk, which is more plentiful and higher in fat and sugar to meet the growing baby's energy needs.

A caveat: because colostrum is produced in small amounts, parents sometimes worry there is “not enough milk.” In fact the low volume is normal and appropriate for a newborn's tiny stomach, and the value of colostrum lies in its quality, not its quantity.