Congenital Hypothyroidism Screening in Term Neonates using Umbilical Cord Blood TSH Values

Congenital hypothyroidism remains one of the most common preventable causes of mental retardation among children. Screening for congenital hypothyroidism remains one of the most cost-effective tools to prevent mental retardation in the population. Umbilical cord blood thyroid-stimulating hormone (TSH) levels remain an attractive and a practical step for screening for congenital hypothyroidism. The aims of this study were as follows: (1) to find normative values of cord blood TSH for the study group and (2) to use cord blood TSH levels as a marker for screening of congenital hypothyroidism. Cord blood of 1824 neonates who were of term gestation, weighed >2.5 kg at birth, whose mothers were off thyroid medication were a part of the study group. Umbilical cord blood was collected at the time of delivery and TSH was estimated. All babies who had a cord blood TSH value of >20 mIU/L were called bay on day 7 of life for a full thyroid profile. Cord blood samples of 1824 neonates were tested for TSH. Male-female ratio was 979:845 = 1.15:1. The birth weights ranged between 2.5 and 4.5 kg with an average birth weight of 2.811 kg. Mean (standard deviation) TSH value was 7.725 (8.99). TSH values ranged between 1.2 and 100 mIU/ml. TSH values corresponding to the 3^rd, 10^th, 25^th, 50^th, 90^th, 95^th, and 97^th percentile were 2.32, 4.05, 5.67, 7.5, 12, 20.63, and 30.88, respectively. Out of the 88 babies recalled for repeat testing, 80 babies only turned up; eventually one turned out to be hypothyroid on repeat testing. The incidence of congenital hypothyroidism in our study was 1 in 1824. To conclude, we can safely use a cutoff of cord blood TSH value of >20 mIU/L for the purpose of screening for congenital hypothyroidism. For logistic angles, a higher cutoff of >30 mIU/L can be used. Large population-based studies are required to establish normative values for cord blood TSH in our country.