PITUITARY-THYROID AXIS FUNCTION IN THE LOW BIRTH WEIGHT INFANT (LBW) WITH INTRACRANIAL HEMORRHAGE (IC)

Abstract

The incidence of hypothyroxinemia low serum thyroxine(T4) and normal serum thyroid stimulating hormone (TSH) levels in the LBW with an IC is significantly greater than in the LBW without IC. The significance of this observation is not clear. The purpose of the study was to assess pituitary-thyroid axis function in the LBW with IC by examining the pituitary and thyroid gland response to thyrotropin releasing hormone(TRH).Twenty-four LBW weighing < 2.0 kg were screened for IC by ultrasonography between days 1 and 7 of life. On day 3, samples were drawn for serum T4 and TSH levels immediately prior to and 30 and 180 minutes after 20 μg/kg TRH IV.Six LBW were identified as having IC. Compared to the LBW without IC, the mean birth weights, 1 and 5 minute Apgar scores and incidence of RDS were similar in both groups. The mean ± SEM gestational age was significantly lower in the LBW with IC (29.5 ± 0.8 vs. 31.2 ± 0.3 weeks, p<0.025). The mean baseline serum TSH and T4 levels were similar in both groups. The mean serum T4 level was significantly greater at 30 and 180 minutes in the LBW without IC. The mean serum TSH level at 180 minutes remained significantly higher in the LBW with IC (51.4 ± 13.1 vs. 21.9 ± 4.0 μu/ml, p<0.01). Conclusion: 1) In response to TRH at 3 days, the mean serum TSH level at 180 minutes in the LBW with IC remains significantly elevated. This response is similar to that seen in patients with hypothalamic hypothyroidism.