Serum thyroxine-like iodine compounds (BEI) are essential for normal central nervous system development, but thyroid function tests of full-term and of low-birth-weight infants have not been defined through 18 postnatal months. For 49 full-term infants (normal BEI through five postnatal days 7.2μg to 15.2μg per 100 ml), median and mean BEI from two to six postnatal months were 6.2 ± 0.91 and from 6 to 18 months 5.8μg ± 0.87μg per 100 ml, significantly higher BEI values than for adults. Differences between BEI means of low-birth-weight infants born before and after 34 gestational weeks and of full-term infants were significant at the 0.001 level. Fifteen low-birth-weight infants with BEI determinations until 19 months were examined developmentally; nine, classified normal, appeared to have increasing BEI; six, classified suspect or abnormal, had low or borderline BEI.
Man EB, Adelman M, Jones WS, Lord RM. Development and BEI of Low-Birth-Weight Infants Full-Term and Through 18 Months. Am J Dis Child. 1970;119(4):298-307. doi:10.1001/archpedi.1970.02100050300003