Whether you'd like to conceive or are trying to avoid pregnancy, it's common to scrutinize yourself for signs of early pregnancy--particularly if you've recently missed a period. Early pregnancy causes many changes in a woman's body and in the way her body functions; some of these changes take place in the breasts.
The medical establishment defines pregnancy as beginning on the first day of your last menstrual period, meaning you're two weeks pregnant before you even conceive. By the time you miss a menstrual period, you're actually four weeks pregnant. For many women, a missed period is the first sign of early pregnancy, though some women experience signs and symptoms as early as within a few days of conception, explain Heidi Murkoff and Sharon Mazel in their book "What To Expect When You're Expecting."
Whether they notice changes to their breasts before or after they notice a missed period, most women's breasts do change significantly in the early days and weeks of pregnancy, explain Murkoff and Mazel. As pregnancy hormone levels increase, your breasts begin to receive more blood, making them swell and become sore. Many women also notice tingling nipples and extra sensitivity. The soreness can be quite intense and uncomfortable.
While breasts begin to change very early in pregnancy, they don't begin to produce milk until after the birth of your baby, explains Dr. Miriam Stoppard in her book "Conception, Pregnancy and Birth." If you're in early pregnancy, your breasts may leak a small amount of clear fluid, though for most women this doesn't happen until well into the second trimester. The clear fluid, called colostrum, is a milk precursor, and you'll continue to make it until several days after childbirth.
If you're breastfeeding one infant when you become pregnant with another baby, you may notice some changes in your breasts. Leaking milk, however, has to do more with the fact that you're nursing an infant than it does with the fact that you're pregnant with a second. Women who are not nursing do not experience any degree of breast milk production or leakage early in pregnancy.
If your breasts are leaking a milk-like substance and you haven't recently given birth, you should contact your physician, regardless of whether you think you might be pregnant. The substance may or may not be milk, and it's important to have any nipple discharge evaluated to determine what it is and what is causing it, explains Dr. Raymond Poliakin in his book "What You Didn't Think To Ask Your Obstetrician."