Bed rest and other determinants of bone loss during pregnancy

Objective The purpose of this study was to evaluate patterns of bone loss during pregnancy and potential influences. Study design This was a prospective study of 181 women receiving prenatal care at Magee-Womens Hospital or its auxiliary clinics in Pittsburgh, Pennsylvania, between 1992 and 1995. Bone mineral density was measured at approximately 16 and 36 weeksʹ gestation. Results Trabecular, but not cortical, bone loss occurred during pregnancy. Mean ultra-distal bone mineral density loss was 1.9% (95% CI 1.2-2.5) during the 20-week period. Women prescribed bed rest had an adjusted mean loss of 4.6% compared with 1.5% for women not prescribed bed rest (P = .001) and 6-fold higher odds (P = .001) of bone loss ≥5% during the 20-week period. Nulliparity, calcium intake <2000 mg/day, low weight gain, and maternal age <21 or >30 years were more modestly associated with greater bone loss. Conclusion Substantial trabecular bone loss may occur during pregnancy, particularly in women prescribed bed rest. Study of postpartum bone recovery in such women is needed.