5. lifting and holding too heavy
More often than none, pregnant women do too much.
4. abnormal Muscle use
When your body changes, you will use your muscles in new ways.
3. Growing uterus
As your baby grows it takes up space and causes the rest of the body to shift out of its way. Your uterus growing inside of you shifts your center of gravity, stretches out your abdominal muscles and weakens them. Thus effecting your overall posture and causes strain to your back.
Progesterone relaxes muscles in the pelvis to allow the pelvic floor muscles to let the baby move through the pelvis.
Relaxin is a hormone that is secreted every time you ovulate. This is because your body anticipates you getting pregnant every time that you ovulate but goes away when you do not conceive. When you become pregnant relaxin continues to secrete your entire pregnancy, allowing your joints to move freely, in hopes of making delivery of the baby easier. (Relaxin helps your hips widen and shift to allow the baby's body to move through the pelvis). In doing so, your joints may ache.