Pregnancy-related back and pelvic pain and changes in bone density

Objective. To elucidate whether there is an association between pregnancy-related back and pelvic pain and changes in bone density. Methods. In this prospective cohort study. bone density was measured in the distal and ultradistal forearm at 12 and 35 weeks of pregnancy and at 5 months post partum. The location and degree of any back or pelvic pain was registered. The patients were classified into four subgroups on the basis of presence or absence of disabling pain in late pregnancy and presence or absence of pain at 5 months' follow-up. Forty-nine women participated. Results. Bone density decreases during pregnancy and lactation. Trabecular bone is mainly lost during pregnancy and cortical bone during lactation. No association between back or pelvic pain during pregnancy and bone loss was found. Between 35 weeks of pregnancy and 5 months post partum, bone loss in all the women was estimated as 1.1% of cortical bone (p<0.001) and 0.6% of trabecular bone (n.s.). During the same period five women with mild pain during pregnancy and pain at follow-up lost 3.9% of cortical bone (p=0.043) and 5.3% of trabecular bone (p=0.043). Although this bone loss was significant compared to the other subgroups, the small study size does not permit general conclusions to be drawn from this finding. Conclusion. The results indicate that bone density decreases during pregnancy and lactation. The decrease in bone density was not associated with back or pelvic pain during pregnancy. It remains unclear whether bone loss is associated with back and pelvic pain during lactation.