Bone histology and mineral homeostasis in human pregnancy.

Mineral homeostasis was studied biochemically and histologically in patients in early pregnancy and at term. In early pregnancy there was evidence of increased and reversible resorption of bone, whereas in late pregnancy bone demonstrated active formation and rapid mineralization with minimal resorption. Gut absorption of calcium was not increased in early pregnancy. The overall findings were consistent with calcium liberation from bone in early pregnancy, and with enhanced conservation of bone calcium at term. It is proposed that the additional calcium required during pregnancy is derived largely from the skeleton during early gestation and from dietary absorption at term.