Do maternal factors influence neonatal thyroid status in the extreme premature infant?

In early pregnancy, maternal transfer of thyroxine (T4) significantly contributes to the foetal T4 requirements. Interruption of the maternal transfer of T4 may lead to inadequate T4 exposure, potentially leading to neurodevelopmental deficits.

To determine if maternal factors are associated with the thyroid hormone status of extremely premature infants during the first five days of life.

This prospective study looked at 117 mothers and their extremely premature babies (born before 28 weeks' gestation). The relationship between neonatal thyroid hormone status and maternal factors (gestation, route of delivery, exogenous maternal glucocorticoid administration, maternal free T4 (FT4), presence or absence of maternal chorioamnionitis, maternal smoking status, maternal body mass index (BMI) index, maternal thyroid peroxidase antibody status (TPO) and maternal haemoglobin levels) were evaluated. Multiple linear regression was used to study independent factors affecting neonatal thyroid function.

Mean gestational age was 25(+5) ± 1.3 weeks (range 22(+0) to 27(+6)). Neonatal FT4 strongly correlated with gestation, with a greater severity of hypothyroxinaemia associated with lower gestation (r = 0.6, p < 0.0001). Multiple regression found gestation to be the only independent factors affecting thyroid status (beta coefficient = 0.08, p = 0.01), and no maternal factors were found to be associated with neonatal thyroid status.

Neonatal thyroid status in extreme preterm infants is independently affected by gestation and not maternal factors such as route of delivery, exogenous maternal glucocorticoid administration, third trimester maternal FT4, presence or absence of chorioamnionitis, smoking status, BMI, TPO status or haemoglobin levels. The severity of neonatal hypothyroxinaemia increases with lower gestational age.