Effect of maternal administration of thyrotropin releasing hormone on the preterm fetal pituitary-thyroid axis

We evaluated the response of preterm fetuses to maternal intravenous injection of 400 μg of thyrotropin releasing hormone (TRH) between 30 minutes and 5 hours before delivery (n=12). An additional seven mothers received saline solution and served as control subjects. There were no statistically significant differences in gestational age, birth weight, or Apgar scores between groups. At delivery, concentrations of maternal thyrotropin were elevated in the TRH group compared with the control group (12.0±1.6 vs 5.6±0.5 mU/L; p 3 ) values remained unchanged. Significant elevations of fetal thyrotropin and T 3 were observed after maternal administration of TRH compared with control subjects (45.8±7.7 vs 8.4±0.9 mU/L ( p p 4 ) and prolactin values were also elevated after exposure to TRH (135±5 vs 86±10 nmol/L or 10.5±0.4 vs 6.7±0.8 μg/dl ( p p 3 but not T 4 levels was observed in both groups of infants. These data indicate that fetal exposure to a single dose of TRH via maternal administration of this hormone results in marked stimulation of the preterm fetal pituitary-thyroid axis, as in the fetus at term, and that this treatment does not inhibit the early postnatal surge of T 3 .