Hypothyroxinemia and effectiveness of thyroxin supplementation in very low birth weight infants with abdominal distension and poor weight gain

Abstract Background Very low birth weight (VLBW) infants sometimes develop abdominal distension and poor weight gain. The influence of thyroid function on these symptoms in VLBW infants has not been reported. Methods In a retrospective study, 18 VLBW infants whose abdominal distension and poor weight gain did not improve with standard treatment were enrolled as subjects. Serum levels of free thyroxin (fT 4 ) and thyroid stimulating hormone (TSH) were measured. Subjects with serum fT 4 levels less than 1.3 ng/dl received thyroxin supplementation. Another 18 VLBW infants were recruited as age- and weight-matched controls. We compared degree of intestinal dilation on X-ray, weight gain, and quantity of milk tolerated before and after starting thyroxin supplementation in the subjects and the controls. Results All subjects had serum fT 4 levels less than 1.3 ng/dl (mean, 0.72 ng/dl). TSH values varied widely and were less than 8 µU/ml in 12 subjects. Therefore, all subjects received thyroxin supplementation; after starting this, mean serum fT 4 level increased significantly to 1.31 ng/dl. In parallel with fT 4 increase, intestinal dilation improved in 16 of 18 subjects (mean grade of dilation decreased from 2.8 to 1.6). Weight gain and quantity of tolerated milk were significantly increased with thyroxin supplementation in all and 17 of the 18 subjects, respectively. Conclusions Thyroxin supplementation was effective in improving abdominal symptoms in VLBW infants whose serum fT 4 level was less than 1.3 ng/dl.