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Fetal bone metabolism in normal and rhesus isoimmunised pregnancies
1Department of Maternal and Fetal Medicine, Chelsea and Westminister Hospital, Imperial College School of Medicine, London, UK.
Objective:
To construct gestation-specific reference intervals for fetal concentrations of biochemical markers of bone metabolism and assess the effect of rhesus isoimmunisation on these.
Methods:
Fetal blood samples were obtained by cordocentesis from 175 pregnancies (43 complicated by rhesus isoimmunisation) and assayed for carboxy terminal pro-peptide of type I pro-collagen (PICP) and cross-linked carboxyterminal telopeptide of type I collagen (ICTP) which directly monitor the rate of bone formation and resorption respectively.
Results:
Both plasma PICP and ICTP were negatively correlated with gestational age (r = -0.351 and -0.472 for PICP and ICTP, respectively, and P < 0.001 for both). In fetuses affected by rhesus isoimmunisation PICP levels were lower (P=0.030) and more variable (P <0.001) than expected, compared with normal unaffected fetuses. However, no such differences were found in the ICTP levels. In the fetuses affected by rhesus isoimmunisation there was a significant correlation between haemoglobin concentration and both PICP (r = 0.504, P = 0.001) and ICTP (r = 0.343, P = 0.030).
Conclusions:
Fetal bone turnover declines from early second trimester to term, and may be deranged in fetuses affected by rhesus isoimmunisation.