Thyrotropin-releasing hormone: Does two hundred micrograms provide effective stimulation to the preterm fetal pituitary gland compared with four hundred micrograms?

OBJECTIVE: Our purpose was to compare the response of the fetal pituitary-thyroid axis to 200 and 400 μg of thyrotropin-releasing hormone administered to the mother immediately before delivery with a control group. STUDY DESIGN: A randomized controlled trial was conducted of 26 women at gestational ages between 24 weeks and 33 weeks 6 days who had received one or more doses of betamethasone who were expected to be delivered within 1 to 4 hours. Women received either 200 or 400 μg of thyrotropin-releasing hormone or were in the control group. RESULTS: Thyroid-stimulating hormone determinations on cord blood had a higher mean level in both treatment groups compared with the control group. No differences were seen in cord blood results between the two treatment groups for thyroid-stimulating hormone, thyroxine, triiodothyronine, free thyroxine, free trioodothyronine, and prolactin levels. The only other differences found were in a higher level in total thyroxine and a lower level of free thyroxine in the 400 μg thyrotropin-releasing hormone group compared with the 200 μg group in the 48-hour blood determinations. CONCLUSION: Both 200 and 400 μg of thyrotropin-releasing hormone provided fetal pituitary stimulation, as reflected in fetal thyroid-stimulating hormone levels in cord blood, and both gave significantly higher levels compared with a control group.