Dynamic changes in serum osteocalcin levels in the perinatal periods

Osteocalcin is a bone-specific protein released into the blood proportional to the rate of new born formation. It is widely accepted that the level of serum osteocalcin is a clinical marker of bone turnover. Nephrogenic cAMP is a specific indirect parameter of the biologically active parathyroid hormone. For analysis of bone metabolism during pregnancy, we measured the concentrations of osteocalcin and nephrogenic cAMP in the maternal serum during pregnancy and in the cord serum at delivery. Nephrogenic cAMP values (n mol/dl GF: mean +/- SEM) increased from the first trimester (1.5 +/- 0.21) to the term (2.11 +/- 0.11). Osteocalcin values (ng/ml: mean +/- S.D.) conversely declined from the first trimester (3.17 +/- 1.66) until the term (1.48 +/- 0.71) and acutely increased in the puerperium (5.91 +/- 2.58). These results might indicate that pregnancy induces a state of secondary hyperparathyroidism, but bone turnover is suppressed. In the cases of uncomplicated deliveries, the concentration of osteocalcin in the umbilical vein was significantly higher than that in the cord artery. This result suggests that a protein immunologically reactive to the osteocalcin antibody might be produced in the human placenta.