Lower Back Pain in Pregnancy

A study published in Nature (1) sheds some new light on lower back pain in pregnancy by studying the evolution of the human spine. Researchers have studied the differences in male and female spines and have also looked at the spines of ancient females – two million years old.

They found that the female spine is different to the male spine and that it is better adapted to pregnancy.  When we first stood up on two legs from all fours we had to develop curves in our spines in order to be able to shift our centre of gravity backwards – so that we didn't fall over all the time. This has led to the characteristic S shaped spine described here.

However, as a pregnancy develops the weight of the baby again moves the centre of gravity forward. To compensate for this women tilt their pelvis forwards to increase the curve at the base of the spine.  This increases the curve by as much as 28 degrees. This posture combined with hormonal changes can lead to lower back pain.

The researchers found however that the female spine has developed some differences to the male spine to cope with this.

• In women the curve or lordosis in the lower back spans a larger area – three vertebrae as opposed to two in men
  
  
• Women’s facet joints are slightly larger (14%) which enables a greater resistance to stress
  
  
• The joints are slightly differently aligned - providing better resistance to forward stresses

The researchers theorise that these adaptations make lower back pain in pregnancy less likely – thus improving our ancient ancestors chances of survival. Interesting and controversial.

Lots more information on lower back pain in pregnancy

1. Whitcome, K. K., Shapiro, L. J. & Lieberman, D. E. Nature advance online publication, doi:10.1038/nature06342 (2007).

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24-Sep-2012