The feto-placental unit stimulates the pregnancy-associated increase in maternal bone metabolism

The aim of the study was to investigate role of the fetoplacental unit in t he pregnancy-induced increase in maternal bone metabolism. To achieve this, circulating concentrations of carboxy terminal pro-peptide of type I pro-c ollagen (PICP, a marker of bone formation) and cross-linked carboxy termina l telopeptide of type I collagen (ICTP, a marker of bone resorption) were m easured in three groups of pregnant women. Group 1 comprised 12 women with singleton pregnancies; group 2, nine women with twin pregnancies; and group 3, 19 women with multifetal pregnancies (greater than or equal to 3 fetuse s) before and after selective fetal reduction to twin pregnancies. Blood sa mples were obtained at 10-12 weeks gestation (groups 1-3, pre-fetal reducti on in group 3) and 4 weeks and 8 weeks later (groups 2 and 3). Before fetal reduction there was a significant correlation between the number of fetuse s and the concentrations of both PICP and ICTP (r = 0.503 and P = 0.001 and r = 0.573 and P < 0.001 respectively). The circulating concentrations of P ICP and ICTP were significantly higher in the pre-reduction multifetal preg nancies than in the twin pregnancies (P < 0.001 and P = 0.0013 respectively ). The circulating concentrations of ICTP in multifetal pregnancies fell by 4 weeks after fetal reduction to those observed in control twins. Concentr ations of PICP were unaltered after fetal reduction. Higher order multiple pregnancies had the greatest decline in ICTP concentrations. These data sug gest that the increased bone turnover observed in the multifetal pregnancie s is due to a factor derived from the fete-placental unit and that this fac tor acts primarily to stimulate bone resorption.