Why Does Pregnancy Cause Low Back Pain?

Health Professional

Mothers-to-be might also expect low back pain too.   A woman's body undergoes so many changes in order to carry a baby to term.   Three specific changes are the reason that low back pain can occur during pregnancy.

The first reason is a very small hormone with powerful effects called relaxin.   This hormone is responsible for relaxing the ligaments, hence the name "relaxin".   Different women produce different levels of relaxin during pregnancy.   With a little extra give to the ligaments that hold the bones together, the baby can travel through the birth canal a little easier.   Depending on the amount of relaxin, different women have various degrees of birth canal relaxation (1).   But the pelvis is not the only place where relaxin affects the skeletal system.   Other ligaments in other parts of the body like the spine are affected too.   The extra amount of flexibility in the spine can make a pregnant woman more vulnerable to low back pain.

In addition to the lack of ligamentous support, a pregnant woman also has to contend with a different posture and more difficulty walking.   As the baby grows, posture changes in various ways.   The mid-back tends to hunch forward more and the low back tends to flatten (2).   All of these changes make it more and more difficult to sit, sleep, and walk.   As movement gets more difficult, low back pain becomes more likely.   And to top it off, pregnant women are more likely to fall too (3).   A fall would only make matters worse, so mothers-to-be tend to naturally compensate for these changes by walking slower with the feet wider apart, especially in the final trimester.   The last trimester is when back pain can really reach a crescendo.

The last trimester is also when the abdominal wall is stretched to the limit.   This wall is the built in back brace for the body and does not work very well when it is ballooned out.   All of the layers of muscle are then no longer able to tighten effectively in order to support the low back during activities like reaching and lifting.   Thus, such activities are best avoided during the final stages of pregnancy.

Pregnancy-related low back pain is very common for all of these reasons.   However, there are certain solutions to pregnancy-related back pain which will be explored in the second part of this series about pregnancy and low back pain.

References:

(1)  MacLennan AH; The role of hormone relaxin in human reproduction and pelvic girdle relaxation; Scandinavian journal of rheumatology, Supplement; 119;88:7-15

(2)   Betsch M; Wehrie R; Dor L; ct al; Spinal posture and pelvic position during pregnancy: a prospective rastersterographic pilot study; Eurpopean Spine Society, The European Spinal Deformity Society, and the European Section of the Cervical Spine Research Society; 2014 Aug 26

(3)   Inanir A; Cakmak B; Hisim Y; Demirturk; Evaluation of postural equilibrium and fall risk during pregnancy; Gait & Posture; 2014 Apr; 39(4):1122-5

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