Postnatal changes in serum osteocalcin and parathyroid hormone concentrations.

Abstract

Cord clamping at birth leads to interruption of calcium (Ca) supply to the fetus. After birth, neonatal parathyroid hormone (PTH) secretion appears stimulated by hypocalcemia, with serum PTH increasing after birth and peaking at 24 hours of age. This rise in PTH presumably leads to bone resorption and Ca release. We theorize that bone formation may also be affected and that a serum marker of bone formation, serum osteocalcin (OC) concentrations, will decrease postnatally. OC is synthesized by osteoblasts and its serum concentrations are believed to reflect bone formation. We measured serum ionized Ca (iCa), PTH, and OC in cord blood and at 2 and 24 hours in 26 neonates born after uncomplicated pregnancies, labors, and deliveries. Serum iCa (mg/dl) decreased from 5.79 +/− 0.06 (cord, means +/− SEM) to 5.31 +/− 0.05 (2 hr), then to 4.89 +/− 0.05 (24 hr) (p less than 0.05). Serum PTH (microliter Eq/ml) increased from 35.9 +/− 4.3 (cord) to 41.7 +/− 4.0 (2 hr) (p = 0.1), and to 50.3 +/− 4.6 (24 hr) (p less than 0.01). Serum OC (ng/ml) decreased from 55.1 +/− 10.6 (cord), to 12.4 +/− 4.3 (2 hr) (p less than 0.01), then remained stable at 12.7 +/− 1.9 (24 hr). The change (cord minus 24 hr) in OC correlated inversely with the change in PTH over the first 24 hours of age (r = -0.42. p = 0.03). Therefore, there is a sudden decrease in an index of bone formation (i.e., serum OC) in the first 24 hours of life in which rising serum PTH may have had an impact.(ABSTRACT TRUNCATED AT 250 WORDS)