Parathyroid hormone and parathyroid hormone-related peptide in venous umbilical cord blood of healthy neonates.

Objective of this study was to assess the role umbilical cord serum parathyroid hormone (PTH), and parathyroid hormone-related peptide (PTH-RP) may play in maintaining the maternal-fetal calcium (Ca) gradient. PTH and PTH-RP and total and ionized Ca levels were measured in blood samples of 20 neonates immediately after birth. Maternal peripheral blood total Ca was measured simultaneously. Mothers were free of hypertension, diabetes or Ca disorders. Neonates were healthy term babies with Apgar scores of eight or greater at one and at five minutes post delivery. PTH was measured using an immunoradiometric double antibody assay that recognizes intact PTH (1-84). PTH-RP was measured by an immunoradiometric double antibody assay that recognizes only PTH-RP (1-74). There was no overlap between the two assays. Ca levels in the neonates were higher than those in their mothers (p < 0.01), confirming a maternal-fetal Ca gradient. However in 18 out of 20 neonates PTH levels in cord blood were below the detection limit (3 pg/ml) and PTH-RP levels also were below detection limit (0.2 pmol/L). PTH-RP and PTH levels in the other two neonates were 0.5 and 0.6 pmol/L (PTH-RP) and 3 pg/ml (PTH) which are in the low normal range for normal adults. We conclude that these data do not support a role for either PTH or PTH-RP in venous cord blood in maintaining the maternal-fetal Ca gradient. They are, however, compatible with a paracrine role for these hormones.