Expectant mothers gain an average of 24 pounds during pregnancy. This weight begins to be distributed toward the front of the abdomen and is believed to cause changes in the way pregnant women walk. Research shows, however, that walking patterns don't change that much over the course of pregnancy. The "waddling gait" believed to happen in late pregnancy isn't that common.
In pregnant women, the muscles of the calf and hip are notably more active during walking. This is thought to contribute to problems of overuse in the leg muscles and may explain why you are feeling cramping in your calves. If your condition keeps giving you problems, let your doctor or physical therapist know.