Background: Thyroid function is dynamic during the perinatal period with many factors potentially influencing maternal, fetal and neonatal TSH and thyroid hormone levels. We sought to identify the impact of numerous maternal, fetal and delivery attributes on thyroid parameters in newborns.
Methods: This was a cross sectional study of 300 newborns. Detailed information was obtained from medical records and multiple characteristics from the record were tested as predictors of cord blood serum total T4, free T4 and TSH and infant T4 levels from the Maryland newborn screening program.
Main outcome: Outcomes are levels of thyroid stimulating hormone (TSH), thyroxine (T(4)), and free T(4) in newborn cord serum and total T(4) in postnatal heelstick bloodspot samples.
Results: Multivariate models identified a number of variables that are independently associated with thyroid hormone levels: higher birth order (lower cord TSH); older maternal age (lower cord total T(4)); pregnancy-induced hypertension and/or preeclampsia (lower cord total T(4) and free T(4)); gestational diabetes (higher cord free T(4)); sexually transmitted disease during pregnancy (lower cord TSH); alcohol use during pregnancy (lower cord TSH); thyroid condition/medications (higher bloodspot total T(4), both neonatal and subsequent); Asian ancestry (higher cord TSH); male sex (higher TSH and lower neonatal bloodspot total T(4)); and C-section (lower cord TSH). Gestational age was independently associated with lower cord TSH, higher cord total T(4), and higher neonatal and subsequent bloodspot total T(4).
Conclusions: Fetal and newborn thyroid hormone levels during the perinatal period are dynamic and influenced by several biological and delivery related factors. Efforts to identify fetal thyroid disruptors in late gestation must carefully consider these factors.