Back pain after the birth can possibly be a continuation of back pain experienced during the pregnancy. However, back pain may also be something that starts happening after the birth, and can be caused by:
Hormones
Weakened abdominal muscles
New 'mothering' activities
Incorrect posture
Incorrect lifting
Hormones. It is possible for the woman to injure her back for the first time during her recovery period after the birth. Traces of the hormone 'relaxin' are present in the woman's body in fairly large quantities up to 6 weeks after the birth, and can remain present for as long as 6 months after the baby is born. Therefore, the ligaments holding the pelvic bones to the woman's backbone at the
sacrum (as well as the pubic bone at the front of the pelvis) will usually remain quite soft, and elastic, for some time. This can give the woman's pelvis mobility and 'slip', making the woman prone to
sciatica, (or
symphysis pain), if her back and pelvis move out of alignment, pinching the nerves.
Overstretching, incorrect posture and/or lifting, twisting and turning suddenly with softened ligaments can easily cause back strain in the early weeks after the birth. It is important to go slowly, allowing your body time to recover, and regain strength again.
Image 1-13 shows the back of the female pelvis and lower spine with the connecting ligaments.
Weakened abdominal muscles. The abdominal muscles are weakened in pregnancy, as they stretched with your growing baby. It will take a while to strengthen them again after the birth. You usually 'brace' your stomach muscles to help you lift objects, and to help you move from a lying or sitting position. If your abdominal muscles are not strong enough to do this, then your body automatically uses your lower back muscles to perform these tasks. This can lead to straining the lower back, and possibly long term back pain.