It's Colostrum not the full milk as that only starts to come in after the baby has been born.
The baby will feed on the colostrum at first and that triggers the full milk production.
An expectant mother's body will in the last few weeks of the pregnancy start producing
colostrum this is a good thing and usually a good indicator that breast feeding will go well
rather then it drying up after the baby arrives.
What is colostrum? How does it benefit my baby?
Your breasts produce colostrum beginning during pregnancy and continuing through the early days of breastfeeding. This special milk is yellow to orange in color and thick and sticky. It is low in fat, and high in carbohydrates, protein, and antibodies to help keep your baby healthy. Colostrum is extremely easy to digest, and is therefore the perfect first food for your baby. It is low in volume (measurable in teaspoons rather than ounces), but high in concentrated nutrition for the newborn. Colostrum has a laxative effect on the baby, helping him pass his early stools, which aids in the excretion of excess bilirubin and helps prevent jaundice.
When your baby is breastfed early and often, your breasts will begin producing mature milk around the third or fourth day after birth. Your milk will then increase in volume and will generally begin to appear thinner and whiter (more opaque) in color. In those first few days it is extremely important to breastfeed your newborn at least 8-12 times each 24 hours, and more often is even better. This allows your baby to get all the benefits of the colostrum and also stimulates production of a plentiful supply of mature milk. Frequent breastfeeding also helps prevent engorgement.
Your colostrum provides not only perfect nutrition tailored to the needs of your newborn, but also large amounts of living cells which will defend your baby against many harmful agents. The concentration of immune factors is much higher in colostrum than in mature milk.
Colostrum actually works as a natural and 100% safe vaccine. It contains large quantities of an antibody called secretory immunoglobulin A (IgA) which is a new substance to the newborn. Before your baby was born, he received the benefit of another antibody, called IgG, through your placenta. IgG worked through the baby's circulatory system, but IgA protects the baby in the places most likely to come under attack from germs, namely the mucous membranes in the throat, lungs, and intestines.
Colostrum has an especially important role to play in the baby's gastrointestinal tract. A newborn's intestines are very permeable. Colostrum seals the holes by "painting" the gastrointestinal tract with a barrier which mostly prevents foreign substances from penetrating and possibly sensitizing a baby to foods the mother has eaten.
Colostrum also contains high concentrations of leukocytes, protective white cells which can destroy disease-causing bacteria and viruses.
The colostrum gradually changes to mature milk during the first two weeks after birth. During this transition, the concentrations of the antibodies in your milk decrease, but your milk volume greatly increases. The disease-fighting properties of human milk do not disappear with the colostrum. In fact, as long as your baby receives your milk, he will receive immunological protection against many different viruses and bacteria.