The effect of pregnancy on bone density and bone turnover

During pregnancy, the mother adapts to meet the calcium demands of the fetu s. The effect of this adaptation on the maternal skeleton is not fully unde rstood. Our objectives were to evaluate changes in bone mineral density (BM D) and bone turnover during pregnancy. We studied 16 women longitudinally, with baseline measurements before pregnancy; then at 16, 26, and 36 weeks o f pregnancy; and postpartum We measured total-body BMD and biochemical mark ers of bone resorption (urinary pyridinium crosslinks and telopeptides of t ype I collagen) and bone formation (serum bone alkaline phosphatase, propep tides of type I procollagen [PINP] and osteocalcin). We also measured parat hyroid hormone (PTH), insulin-like growth factor I(IGF-I), and human placen tal lactogen. Postpartum, BMD increased in the arms (2.8%, P < 0.01) and le gs (1.9%, P < 0.01) but decreased in the pelvis (-3.2%, P < 0.05) and spine (-4.6%, P < 0.01) compared with prepregnancy values. All biochemical marke rs, with the exception of osteocalcin concentration, increased during pregn ancy. The change in IGF-I at 36 weeks was related to the change in biochemi cal markers (e.g., PINP, r = 0.72, P = 0.002). Pregnancy is a high-bone-tur nover state. ICE-I levels may be an important determinant of bone turnover during pregnancy. Elevated bone turnover may explain trabecular bone loss d uring pregnancy.