Concentrations of serum markers of type I collagen synthesis and degradation and serum osteocalcin in maternal and umbilical circulation.

Measurement was made of the serum carboxyl-terminal propeptide of type I procollagen (PICP), carboxyl terminal cross-linked telopeptide of type I collagen (ICTP) and osteocalcin in 17 full-term mother-infant pairs and 17 age-matched nonpregnant women. Serum PICP and ICTP of term women at the time of delivery were significantly higher (P < 0.025, P < 0.01, respectively) and serum osteocalcin was significantly lower (P < 0.001) than in nonpregnant women. The ratio of PICP to ICTP was essentially the same for term and nonpregnant women. Serum PICP, ICTP, and osteocalcin were virtually the same in the umbilical arteries and vein. PICP, ICTP, and osteocalcin were much higher in fetal than maternal circulation (P < 0.001). The fetal levels of these proteins were not correlated with maternal levels, nor with birth weight. Thus, during pregnancy, either osteoclastic or osteoblastic activity would appear to increase slightly, but the balance between bone formation and resorption is maintained. During fetal life, bone turnover may be greatly accelerated and bone metabolism may occur independently of maternal bone metabolism.