Roy Pitkin, M.D., is a professor of obstetrics and gynecology and is the former chair of the ob/gyn department at the University of California, Los Angeles School of Medicine. He is a frequent advisor to national health agencies on women's health issues and has received numerous international honors for this work.

Q: I'm in my second trimester and have been experiencing intermittent pain on both sides of my abdomen, though it most often occurs on the right side. Should I be worried?

A: It's fairly common for women in the middle or latter part of pregnancy to experience intermittent pains in the lower abdomen, usually on the right. These pains are thought to be due to contractions of the muscle in the round ligaments, small bands containing muscle and fibrous tissues that run from either side of the uterus to the abdominal wall. As the uterus grows, the round ligaments are stretched and in response, the muscles contract and cause pain.

The reason for the right-sided predominance may be that the uterus tends to rotate toward the right as it expands. This explanation is entirely theoretical but it seems logical. What is known for sure is that women often experience sharp intermittent pains in the lower abdomen, without any apparent effects on the course and outcome of pregnancy.