Fetal calcitropic hormones and neonatal calcium homeostasis.

Ionic calcium (Ca2+), total calcium, magnesium, phosphorus, albumin, immunoreactive parathyroid hormone (PTH), and immunoreactive calcitonin (CT) were measured in maternal and cord blood at term delivery of 96 women near term with predominantly normal pregnancies. Calcium, magnesium, phosphorus, and albumin were measured in the infants at 24 hours of age. Umbilical Ca2+ levels exceeded maternal values significantly (2.82 +/- 0.15 vs 2.23 +/- 0.09 mEq/liter, P < .001), as did calcium, magnesium, phosphorus, and albumin levels. The relative fetal hypercalcemia was associated with significantly higher CT levels in fetus than in mother (248 +/- 68 vs 209 +/- 54 pg/ml, P < .05) but PTH concentrations did not differ significantly between the two circulations. Within the fetal circulation, levels of each component did not differ except for PTH which was in higher concentration in venous than in arterial blood (5.50 +/- 1.81 vs 4.93 +/- 1.71 microliter-eq/ml, P < .05). Stepwise multiple regression analysis, utilizing neonatal Ca level as the dependent variable, identified one clinical feature (duration of pregnancy) and six laboratory data as significant independent variables, account in sum for 35% of the variation in neonatal calcium level. The significant laboratory variables, in order of entry into the model, were maternal PTH, umbilical venous PTH, maternal phosphorus, umbilical venous magnesium, neonatal albumin, and neonatal magnesium. These results indicate that the normal fetus responds to hypercalcemia in late intrauterine life by increasing CT secretion but not by suppressing PTH output. The umbilical PTH level is one of several factors at birth which correlates significantly with calcium concentration at 24 hours of age.