As early as the first trimester, hormonal changes relax the ligaments supporting the spine and pelvic girdle — the bowl-shaped complex of bones that connects the legs to the trunk and holds the pelvic organs. “Even by week 10 or 11, when you generally aren’t even showing, you can develop laxity, or looseness, in the ligaments,” says Dr. Hameed. That can lead to pain at the top of the buttocks that may shoot down the leg.
As the baby grows, “There’s a shift in the center of gravity that increases stress to the lower back,” Dr. Hameed says. That can lead to an exaggerated curve of the spine, called lordosis, which puts pressure on the muscles and joints in the lower back, triggering pain.
In other cases, pregnancy can affect posture, leading some to round their mid-to-upper back forward, called kyphosis, as the breasts grow during pregnancy and postpartum, producing discomfort in the mid-back and/or neck. At the same time, the expanding uterus strains the abdominal and pelvic floor muscles, creating instability in the core.
The good news is that back pain during pregnancy often resolves a few weeks after the birth, says Dr. Hameed. “Within six to 12 weeks, most women are feeling pretty much back to normal in most ways,” she says (though it may take longer for those who had a C-section).
Some mothers, however, experience new stresses on their body after childbirth due to bending up and down to put infants in the crib or bath and trying to find comfortable positions to nurse, says Dr. Hameed. You may experience new pain in the mid-to-upper or lower back pain as well as neck pain as a result. “Exercise and working on postural awareness can help improve these symptoms as well,” she says.