When I was pregnant with my first child I had terrible back pain that went away when my son was born. My younger sister just had a baby. She had no back pain during the pregnancy, but now she has low back and pelvic pain. Is this hereditary?

Studies show that up to 50 percent of all pregnant women have some kind of back and/or pelvic pain during pregnancy. Most of the time, the pain goes away in the first three months after the child is born. A fair number of women end up with chronic pain that lasts months to years.

Pain after pregnancy is also common. The causes for both kinds of pain patterns are probably different for each woman. Pain during pregnancy that goes away afterwards may be linked to the position of the baby in utero. Pressure from the weight of the child can cause nerve pain or hip, sacroiliac, or back pain. Once the baby is delivered to the outside world, the pressure is gone and so is the pain.

Researchers know that the hormone relaxin is present in greater amounts during pregnancy. It's likely this hormone helps the muscles, ligaments, and other soft tissues relax. This allows the pelvic bones to expand and make room for the baby during delivery. Pain that occurs after pregnancy may be related to the changes in the soft tissue structures. Weakness and instability of the muscles around the abdomen, hip, pelvis, and back often bring about this kind of problem.

Whether these conditions are a normal part of pregnancy or in fact, hereditary remains unknown.