Thyroid Hormone Levels in Diabetic Mothers and Their Neonates

ABSTRACT Infants born to diabetic mothers have decreased activity of many metabolic pathways which might be regulated by thyroid hormone. Serum TSH, T 4 , T 3 / and reverse T 3 levels were measured in 22 term infants of diabetic mothers and in 9 normal term babies at 2, 12, 24, and 72 hours of age, as well as in maternal and cord sera. T 4 binding index and free T 4 levels were measured in 11 diabetic mothers and their babies and 5 normal mothers and babies. Mean TSH levels did not differ between diabetic and normal mothers or their infants. Mean T 4 of the diabetic mothers (9.6 μg/dl) was significantly (p < 0.005) less than the mean T 4 of the normal mothers (12.8 μg/dl). Mean T 4 of neonatal specimens was lower in infants of diabetic mothers for each determination, but this difference achieved statistical significance at the 12-hour sample only (p < 0.001). Mean serum T 4 binding index was similar in the neonatal specimens at each time period studied. Mean T 3 of diabetic mothers (149 ng/dl) was significantly (p < 0.001) less than that of normal mothers (217 ng/dl). At each time interval, mean T 3 concentration in infants of diabetic mothers was significantly lower than that of normal infants. Levels of reverse T 3 were not significantly different between normal and diabetic mothers or their neonates. These data suggest that there is an effect of maternal diabetes on T 3 secretion or conversion of T 4 to the more active hormone, T 3 , in the fetus and early newborn. Furthermore, these data lead to the speculation that some of the metabolic alterations seen in neonates born to diabetic mothers may be due to decreased thyroid hormone levels in utero and during the first days of life.