Is it normal to secrete milk from the breast prior to delivery?

Galactorrhea (milk secretion from the nipple) is the product of the combined effects of prolactin, glucocorticoids, progesterone, and human placental lactogen. Galactorrhea is not uncommon in the first trimester, although it usually does not occur until milk let-down soon after delivery. At that time, the high levels of progesterone, which block milk excretion, drop with the delivery of the placenta. In mid pregnancy a woman reaches lactogenesis stage I and she is able to secrete colostrum.

Early galactorrhea does not mean that a woman will produce less milk after delivery. Some women notice secretions beginning before the fifth month of pregnancy. Many women find they spontaneously leak or express some fluid by the ninth month.

The milk secretion is known as colostrum and is watery and pale. Colostrum has more protein and lower fat than mature milk.

Lactogenesis stages II and III occur postpartum and form more mature milk.

Source: http://emedicine.medscape.com/