Back pain symptoms and bone mineral density changes in pregnancy as measured by quantitative ultrasound.

OBJECTIVE: To evaluate whether back pain symptoms in pregnancy are associated with bone mineral density (BMD) changes as measured by quantitative ultrasound at the os calcis. METHODS: Consecutive patients were recruited from a general obstetric clinic over 1 year. Quantitative ultrasonographic measurements of BMD were performed at the os calcis between weeks 14-20 and 36-38. They were then surveyed for back pain symptoms experienced during pregnancy in the early postpartum period, and these were subsequently correlated with BMD changes. RESULTS: Of a total of 463 patients, 231 (49.8%) reported one or more episodes of significant back pain during pregnancy. A mean fall in BMD of 0.0395 g/cm(2) was demonstrable from early to late gestation. Those with back pain symptoms have higher mean BMD loss at the os calcis during pregnancy compared to those without back pain (0.038 vs. 0.029 g/cm(2); p = 0.012). A logistic regression model showed that weight gain and BMD loss in pregnancy were significantly associated with back pain symptoms. CONCLUSION: Back pain symptoms in pregnancy were associated with a greater fall in BMD at the os calcis, supporting the hypothesis that BMD changes could have an etiological role in back pain during pregnancy.