Effects of antenatal thyrotropin-releasing hormone on fetal heart rate and breathing movements

Objective: To determine the effect of maternally administered thyrotropin-releasing hormone (TRH) on fetal heart rate (FHR) pattern and fetal breathing movements (FBM). Methods: Prospective observational study of 75 pregnant women between 26 and 34 weeks' gestation in whom pharmacological fetal lung maturation was clinically indicated. Forty-minute recordings were made of FBM or FHR patterns before and after drug administration. Twenty-five received TRH 400 mu g as an intravenous bolus, 25 TRH 400 mu g in 50 ml 0.9% saline as an intraveous infusion, and 25 acted as controls. Recordings were processed digitally to calculate the change in FHR (n = 45) and FBM parameters (n = 30). The main outcome measures for FHR were number of accelerations and decelerations, baseline rate, overall and short-term variation and duration of high and low variability, while for FBM they were rate, breath-to-breath interval and incidence. Results between groups were compared by analysis of variance. Results: There was no significant change in FHR, accelerations or variation in any of the groups. Similarly, there was no change in the incidence of FBM. TRH administered as a bolus produced a small statistically but not clinically significant increase in breathing rate (mean Delta = 35 breaths/h, p = 0.004), which was not seen in the TRH infusion and control groups. Conclusions: Maternally administered TRH as used to enhance fetal lung maturation has no clinically significant direct effect on FHR or FBM patterns.