Lowered serum Ca, blood ionized Ca, and unresponsive serum parathyroid hormone with oral glucose ingestion in infants of diabetic mothers.

Oral glucose ingestion may lower serum Ca in infants of diabetic mothers (IDMs). Six metabolically stable IDMs were studied following ingestion of 1.7 +/- 0.1 g/kg (mean +/- SE) of glucose over 20 min and serum Ca, Mg, P, blood iCa, serum PTH, and CT were measured at 0, 1/2, 1, and 2 h. Data obtained in IDMs were compared with previously reported findings in 10 normal neonates. In IDMs as in normal neonates, serum Ca, Mg, P declined significantly after oral glucose ingestion. Blood Ca2+ was significantly lower at +1/2 h in IDMs versus normal neonates, and by analysis of covariance, trends in blood Ca2+ were significantly different in IDMs versus normal neonates, (p less than 0.05). Serum PTH concentrations were unaltered in IDMs versus a significant rise in serum PTH noted in normal neonates. The difference between the two groups was significant statistically (p less than 0.05). Baseline serum CT was elevated in both groups and did not change. Thus, in IDMs responses to oral glucose ingestion differs from that seen in normal neonates as follows: blood Ca2+ is lowered in IDMs versus normal neonates, and serum parathyroid hormone (PTH) does not respond to a decline in blood Ca2+ in IDMs, whereas in normal neonates serum PTH rises and blood Ca2+ is maintained. We speculate that relative parathyroid gland unresponsiveness occurs in IDMs, which may result in lowered blood Ca2+ after oral glucose ingestion in these infants.