The average pregnant woman will gain between 25-35 lbs most of which is focused on the abdomen. This localization of weight puts additional stress on the back, pelvis and legs. This weight gain also changes the centre of gravity and can significantly alter the biomechanics of how we walk, sit, and stand. I know most of us can visualize a pregnant woman extended backwards and waddling to get around properly.
Another factor to consider is a hormone called relaxin that gets released in the second trimester. This hormone is designed to allow the ligaments of the pelvis to expand to accommodate the growing baby and to prepare for the birth process. Where this becomes of concern however is that relaxin doesn’t just target those specific ligaments but rather all our ligaments which very often can lead to joint instability, sprain, and increased strain of the supportive musculature. This then can result in pain, limited mobility and difficulty performing normal daily activities.