Independent Associations among Maternal Alcohol Consumption and Infant Thyroxine Levels and Pregnancy Outcome

Studies with animal models of alcohol-related birth defects (ARBDs) suggest that reductions in circulating thyroid hormones, including thyroxine (T₄), may be a persistent postnatal effect of fetal alcohol exposure. The few clinical reports of children with fetal alcohol syndrome (FAS) that address thyroid system function generally reported that FAS children have thyroid hormone levels within normal limits. For the current study, data bases from the Fetal Alcohol Research Center and the Michigan Department of Public Health Newborn Screening Program were assessed to correlate measures of maternal drug use during pregnancy and infant outcome (gestational age at birth, birthweight, “fetal growth”), with infant whole-blood T₄ levels. Multiple regression analyses accounted for demographic factors, infant age at testing, and variation in the T₄ assay. As expected, alcohol intake and smoking each had a substantial negative impact on birthweight, gestational age at birth, and fetal growth, assessed as birthweight corrected for gestational age. Infant T₄ levels were positively related to birthweight and gestational age and were more strongly related to fetal growth. Infant T₄ levels were not influenced significantly by either maternal smoking or alcohol consumption. Smoking- and alcohol-related reductions in birthweight, gestational age, or fetal growth were not associated significantly with variations in infant T₄. Interesting questions remain regarding species differences and the influences of maternal alcohol consumption on T₄ metabolism as a mechanism for ARBDs. However, the current data do not support the hypothesis that maternal alcohol consumption, or smoking, during pregnancy leads to compromised thyroid system function in newborn humans. Therefore, newborn screens for T₄ are not likely to be effective in helping to detect infants with ARBDs or FAS.