Plasma parathormone (PTH) and calcium concentrations were measured in 309 specimens collected from 190 newborns during the first 7 days of life. The patient material consisted of 51 preterm, 130 term, and 9 postterm infants, including 22 infants of diabetic mothers (IDM), 38 infants with hypocalcemia, and 25 asphyxiated infants. PTH was detectable, although in low concentrations, in cord blood samples despite the presence of elevated calcium concentrations. Postpartum, PTH concentrations in term, appropriate for gestational age (AGA) infants remained low during the first 2 days of life; a significant (P < 0.05) and sustained increase in plasma hormone levels was noted starting on day 3. PTH concentrations in IDM and preterm infants remained low for 3 days and a significant hormone increase did not occur until day 4.Speculation
Basal PTH secretion is present at birth, several days before the parathyroid glands appear to become responsive to hypocalcemia. Furthermore, in cord blood PTH is detectable in spite of elevated calcium concentrations. The present observations suggest that nonsuppressible PTH secretion, previously described in short-term animal experiments, also occurs in the human fetus exposed to long-standing intrauterine hypercalcemia, with the implication that PTH secretion in man may be regulated by control mechanisms in addition to calcium feedback. There is anatomical and pharmacologic evidence to implicate the autonomic nervous system in this control.