During pregnancy, a woman can gain anywhere from 19-30 pounds, with most of the weight being added to the trunk region. This increase in mass occurs relatively quickly, and this rapid change in body weight can cause increased stress on certain parts of the body. Research has shown that the increase in mass in the front of abdomen resulted in increased stress in multiple muscles all across the body, and not just at the pelvic region. When muscles are stressed in ways they normally are not, the function of these muscles can be impaired, which in turn can lead to pain and symptoms.
References:
https://www.degruyter.com/downloadpdf/j/physio.2009.17.issue-3/v10109-010-0019-6/v10109-010-0019-6.pdf
https://www.linkedin.com/pulse/postural-changes-pregnancy-beyond-teresa-chartrand