Effects of methadone on thyroid function in mother, fetus, and newborn

The effects of maternal use of methadone during pregnancy on tests of thyroid function were studied in 14 women and their offspring. Twelve normal nonaddicted women and their infants served as a control group. Concentrations of thyrotropin (TSH), thyroxine (T4), and triiodothyronine (T3) were not significantly different in maternal and cord serum, and in infant serum at age 24 hours. There was no significant difference in infants' TSH concentrations at 2, 3, and 7 days of age. At 2 and 7 days, T3 levels were significantly higher in the methadone than in the control group (P = .01 and less than .01, respectively). At 3 days, differences were of borderline significance (P = .08). Increased T4 levels in the methadone group of infants were statistically significant at 2 days (P less than .01) and at 3 and 7 days (P = .05). The mechanisms responsible for the biochemical evidence of hyperthyroidism were not determined, but may have been related to altered autonomic function and/or increased metabolic activity which occurs during neonatal narcotic withdrawal.