1st trimester

By 6-8 weeks, your breasts may be noticeably larger. Breast growth during pregnancy is due to your body getting ready to breast-feed. The fat layer and milk glands are increasing. Your breasts will continue to grow in size and weight throughout the first trimester. 

Your breasts may feel firm and tender during the first few months of pregnancy. The blood supply in your breasts is increasing and the veins will get larger and more noticeable. You may feel some tingling and your breasts may be sensitive to touch. Wear a supportive bra that fits well. 

Your nipples and areolas (the darker skin around your nipples) will darken. Your nipples may stick out more now. Your areolas will grow larger. On the surface of the areolas you may notice small bumps. These are small glands called Montgomery tubercles which produce an oily substance to help your nipples from cracking or drying out while you nurse. 

2nd trimester

By about 12-14 weeks of pregnancy, your breasts may start making colustrum. This doesn't happen in every woman, so do not be concerned if you don't start producing colustrum until after delivery. Early in pregnancy, the colustrum will probably be thick and yellow. Toward the end of pregnancy, it will change to pale and nearly colorless. Colustrum may leak during breast massage or during sexual arousal. 

To learn more about breast-feeding, click here.