Not everyone has sore breasts in pregnancy in pregnancy, but many women do. Soreness and sensitivity are likely caused by increased blood flow to your chest—which is a result of surging hormones. Sore breasts can start in early pregnancy and typically last until the end of the first trimester. Of course, some people with sensitive breasts may feel changes in the second and third trimesters too. As with most pregnancy symptoms and side-effects, the experience varies from woman to woman and pregnancy to pregnancy.