Gestational diabetes mellitus is a known driver of maternal and neonatal complications, but its effect on newborn thyroid function has been uncertain.

An observational cohort study published in Endocrine Connections linked national newborn screening thyroid data with hospital records from 101,450 mother–infant pairs. The analysis included 4,643 GDM pregnancies (4.6%) and 96,807 non-GDM pregnancies, all term singleton livebirths. Maternal GDM was the primary exposure, and neonatal total thyroxine (TT4) on newborn screening was the main outcome.

Median TT4 was modestly higher in GDM infants (14.9 vs 14.6 μg/dL), but proportions requiring reflex-TSH testing were similar, indicating no clinically meaningful thyroid differences. By contrast, GDM mothers were older (34.2 vs 32.5 years), had higher prepregnancy BMI (25.6 vs 22.5 kg/m²), and faced greater odds of hypertension and proteinuria. GDM pregnancies also showed increased risks of cesarean delivery, large-for-gestational-age infants, and neonatal intensive care admission.

In multivariable models, parity, neuraxial anesthesia, oxytocin use, cesarean delivery, maternal fever, newborn sex, gestational age, and birthweight percentiles were associated with TT4 levels. Overall, GDM was not linked to clinically significant differences in neonatal TT4. Thyroid alterations in term infants of GDM mothers are unlikely to be a concern, although maternal and neonatal complications remain elevated.