Changes in thyroid status in newborn infants utero-exposed to ritodrine.

A clinical study to assess whether utero exposure to ritodrine influences thyroid status was performed in 21 healthy term newborn infants, 10 exposed in utero to ritodrine (treated group) and 11 non-exposed in utero to drugs (control group). The treated group had a T3/T4 ratio significantly higher than the control group (mean +/- SD: 124.10 +/- 23.70 vs. 96.09 +/- 18.11, p less than 0.005) and T3 slightly increased (mean +/- SD nmol/l 2.48 +/- 0.69 vs. 1.95 +/- 0.56). The mean serum values of the other parameters studied, TSH, T4, fT4, fT3, were not significantly different in either groups. Since beta-mimetics induces deiodinating activity of the liver and propranolol reduces extrathyroidal conversion of T4 to T3, it was suggested that ritodrine enhances deiondinating activity of fetal and neonatal liver.