Bone turnover from early pregnancy to postweaning

Background. To elucidate the sequences of changes in bone metabolism and bone density during pregnancy, lactation and postweaning. Methods. Women were recruited (n = 254) in early pregnancy and followed for 2 years. Markers of bone formation (osteocalcin) and resorption (NTx) were measured at five occasions. Bone mineral density (BMD) of whole-body and lumbar spine L-1-L-4 (DXA) and ultrasonography of os calcis were measured in a subgroup (n = 14). Results. NTx appeared bone specific in comparison to pyridinolines. NTx started to increase early in pregnancy and remained elevated during lactation (p < 0.001). Osteocalcin was low during pregnancy, but peaked during lactation (p < 0.018). The subsequent decrease was associated with time since resumption of menses (r(2) = 0.23; p < 0.001). There was indication of a decrease in calcaneal bone mass during pregnancy and an evident decrease in lumbar spine (p = 0.041) and os calcis (p = 0.037) during lactation. No detectable decrease was identified in whole-body BMD (p = 0.090) during lactation, but in general, BMD was higher in whole-body (1.9%) and lumbar spine (6.6%) 18 months postpartum than during puerperium (p = 0.003). Conclusion. According to the bone metabolic markers, bone resorption increased early in pregnancy and remained elevated over lactation, while bone formation increased during lactation, probably regulated by mechanisms associated with absence of menses. The high metabolic bone turnover during late pregnancy and lactation lead to a decline in cancellous bone mass during lactation, but this seemed beneficial for BMD postweaning.