Hormones cause the pelvic ligaments to stretch and the hip and pelvic bones to spread and separate during the second trimester of pregnancy, according to familydoctor.org. This continues into the third trimester, when labor becomes imminent.
Some discomfort may be felt when the pelvic and hip bones start to spread, and the lower back, abdominal and hip areas may feel achy or sore. To relieve pain, the Mayo Clinic suggests practicing good posture by standing straight and tall, holding the chest high, keeping the shoulders relaxed and avoiding locking the knees. Low-heeled shoes with good arch support may help relieve stress in the back and pelvic areas. Lifting large objects should be avoided. Small objects may be lifted by squatting and using the legs. Sleeping on one side with both knees bent and using support pillows between the knees, under the abdomen and behind the back offer relief during slumber.