Typically, if you leak breast milk, it is no more than a few drops at the time. It might be yellowish in color, like butter milk, and it's going to be very thick. Some women start leaking colostrum as early as the first trimester of pregnancy, but leaking breasts are mostly a third trimester symptom. If you are leaking substantial amounts of milk, you can try using breast pads to keep your clothes from getting wet. Colostrum is your first milk, and it contains everything your baby needs in the first few days of life. It contains a myriad of antibodies that serve to protect your baby from infections and diseases, and colostrum also has more proteins and fat than the breastmilk you will start producing some time after birth. Colostrum is the perfect way to deliver many nutrients to your baby in a small concentration, given the fact that the digestive system is still imperfect and the stomach tiny. For more about breast changes in pregnancy, see sore and tender breasts.
When you see that your breasts have started leaking colostrum, the first you will ever produce for your baby, it might come as a bit of a shock. If this happens to you, you are probably in your third trimester. Leaking a bit of milk is a sign that your body and your breasts are working just the way they should be, but it is not unusual not to notice any colostrum until after your baby is born, either. During pregnancy, your breasts will undergo many changes and they might feel sore, get bigger in size, and your nipples may change color. Leaking a bit of milk is the last stage of these changes, and it shows you that your body is ready to breastfeed when you give birth.