The impact of subclinical hypothyroidism on growth and development in infants and young children aged 0 to 5 years

Introduction: The objective was to investigate the growth and development of infants and young children with mild subclinical hypothyroidism aged 0 to 5 years, especially those aged 0 to 2 years.

Material and methods: The study was a retrospective analysis of the birth status, physical growth, and neuromotor development of patients aged 0 to 5 years, who were diagnosed with subclinical hypothyroidism during newborn screening (NBS) in Zhongshan between 2016 and 2019. Based on preliminary results, we compared 3 groups: with thyroid-stimulating factor (TSH) value of 5-10 mIU/L (442 cases), TSH value of 10-20 mIU/L (208 cases), and TSH above 20 mIU/L (77 cases). Patients with TSH value above 5 mIU/L were called back for repeat testing and were divided into 4 groups as follows: mild subclinical hypothyroidism group 1 with a TSH value of 5-10 mIU/L in both initial screening and repeat testing; mild subclinical hypothyroidism group 2 with TSH value above 10 mIU/L in initial screening; and TSH value of 5-10 mIU/L in repeat testing; the severe subclinical hypothyroidism group with TSH value of 10-20 mIU/L in both the initial screening and repeat testing and the congenital hypothyroidism group.

Results: There were no significant differences in the maternal age, type of delivery, gender, length, and weight at birth between the preliminary groups; however, the gestational age at birth was significantly different (F = 5.268, p = 0.005). The z-score for length at birth was lower in the congenital hypothyroidism group compared to the other 3 groups but showed no difference at 6 months of age. The z-score for length in mild subclinical hypothyroidism group 2 was lower compared to the other 3 groups but showed no difference at 2-5 years of age. At 2 years of age there was no significant difference in the developmental quotient (DQ) of the Gesell Developmental Scale between the groups.

Conclusion: The gestational age at birth affected the neonatal TSH level. Intrauterine growth in infants with congenital hypothyroidism was retarded compared to that of infants with subclinical hypothyroidism. Neonates with a TSH value of 10-20 mIU/L in the initial screening and a TSH value of 5-10 mIU/L in the repeat testing showed developmental delay at 18 months but caught up at age 2 years. There was no difference in neuromotor development between the groups. Levothyroxine in patients with mild subclinical hypothyroidism is not required, but we recommend that the growth and development of such infants and young children continues to be monitored.