A woman’s body changes almost as much as that of her growing fetus during pregnancy. Her breasts grow and become capable of producing milk, her hair and nails lengthen and strengthen, her back changes slightly in its overall curvature, and her blood volume increases. One of the changes an expectant mother experiences that’s most obvious to others, however, is that her belly grows increasingly as her pregnancy progresses.
First Trimester
Until about the twelfth or thirteenth week of pregnancy, a woman’s belly is nearly unchanged from its pre-pregnancy state. While the uterus is growing tremendously to accommodate the fetus, it’s no larger than a grapefruit until late in the first trimester, note Heidi Murkoff and Sharon Mazel in their book, “What To Expect When You’re Expecting.” As such, the uterus is tucked into its normal position behind the pubic bone, and first-trimester pregnant women don’t appear visibly pregnant. Some women may have a bit of an expanding waistline early on, due to the bloating and constipation that typically mark early pregnancy, but the appearance of a “baby bump” in the first three months isn’t actually due to a baby; it’s just the intestines protruding a bit.
Second and Early Third Trimester
Around the start of the second trimester, note Murkoff and Mazel, a woman’s belly begins to round and protrude significantly. This is because the uterus has expanded to the point that it can no longer be contained completely behind the pelvic bone, and the top of the uterus pokes out over the bony ridge. Many women are able to feel a round, firm organ near their bikini line starting around the thirteenth week of pregnancy. As pregnancy progresses and the fetus continues to grow, the uterus stretches with it, rising further and further into the abdominal cavity and farther out away from the mother’s body.
Final Month
Around the 36th week of pregnancy, a woman’s belly undergoes one final change, explains Dr. Miriam Stoppard in her book, “Conception, Pregnancy and Birth.” The fetus, which up until this point has been able to turn relatively freely in the uterus, begins to settle into its final head-down position as the time of delivery nears. This serves two purposes. Not only is the uterus becoming quite crowded as the fetus nears full-term size, making movements restricted, but babies are delivered most easily when labor commences with a baby positioned head down. The movement of a fetus into this position is referred to as the fetus descending, and women may notice a visible difference in their bellies—a sense that the bulk of the belly has moved down and closer to the body—as this event takes place.
References
- “What to Expect When You’re Expecting”; Heidi Murkoff and Sharon Mazel; 2008.
- “Conception, Pregnancy and Birth”; Miriam Stoppard, M.D.; 2008.
