Congenital hypothyroidism has a worldwide incidence of 1 in 4000. A higher incidence has been reported from India [1]. The objective of our study was to ascertain the incidence of congenital hypothyroidism in South Malabar area.

Our study was conducted in a tertiary care hospital in Calicut, Kerala. We conducted a retrospective analysis of umbilical cord thyroid stimulating hormone (TSH) values. All inborn deliveries – from October 2012 to October 2013 – in a tertiary care hospital in Calicut, Kerala, were included. TSH, FT4 and FT3 were assayed by chemiluminiscent immunoassay method. A mixed cord blood sample obtained soon after birth was sent immediately for assay TSH. All cord blood TSH values of more than 10 mU/L were followed up at 72 hours of age with a repeat TSH estimation. Those babies with a rising trend in TSH were evaluated with TSH, FT4 and FT3 on day 5 of life. Subsequent follow up was done at 2 weeks of age in individual cases. Congenital hypothyroidism was diagnosed if TSH on day 5 was >40 mU/L with a low FT4 or if at 2 weeks of age the TSH >10 mU/L with low FT4 [2]. Radio nuclear scanning was not done in all cases prior to treatment. Data retrieved from electronic medical records were analyzed by SPSS version 16.

We excluded 120 cases from the analysis, which included perinatal deaths, those lacking adequate follow ups, and those where a proper cord blood sample could not be obtained. Total numbers of samples included in the analysis were 1950 (1268 female) out of which 1551 were term and 397, preterm. Median cord blood TSH value was 6.5 mU/L. Based on our policy of rescreening those with a cord TSH of >10 mU/L, 403 babies needed rescreening at 72 hours. Upon rescreening at 72 hrs, 41 babies had a rising trend in TSH. Out of these 41 cases, eight cases were diagnosed to have hypothyroidism on follow-up; six on day 5 and two on day 14. Cord blood TSH values and the number of hypothyroidism cases within each group are provided in Table I. Congenital hypothyroidism was diagnosed in 8 cases.

TABLE I Distribution of Hypothyroidism Cases According to Cord Blood Tsh Levels

Cord blood TSH was >20 mU/L in all samples, except one where it was 18 mU/L. One baby showed a goiter in radionuclide scanning, whereas maternal hypothyroidism was present in two infants, and maternal hyperthyroidism in one child. No specific cause was found in the other five babies.

A cord blood cut-off of 20 mU/L is considered reasonable but it might be prudent to rescreen babies with a cord blood TSH above 10, as one of our patients had a cord blood TSH of 18 mU/L. Taking a cord blood TSH of 10 mU/L as cut off, our false positivity was 20%. Results from this study population show a higher incidence of congenital hypothyroidism than that has been reported from other countries [3-5] or from other parts of India [1,6,7]. Increase in incidence within the same country over subsequent years also has been reported [8]. The incidence of primary hypothyroidism vary depending on dietary iodine sufficiency, laboratory methods of screening, different test cut-off values, and demographic, geographic, racial and ethnic factors. Social customs like consanguinity also alter the incidence [9]. Transient hypothyroidism also may contribute to varying prevalence [4]. Cord blood TSH provides a suitable first line diagnosis congenital hypothyroidism, especially when a 72-hour screen cannot be ensured. This study has limitations of being a hospital-based retrospective study. In view of higher incidence reported here, prospective studies on a larger population are needed to confirm the findings and elucidate the reasons for the increased incidence.

Contributors: AMR: conceived and designed the study, data collection and analysis, and manuscript preparation. He will act as the guarantor; PR and DN: data collection and preparation of the manuscript. The final version was approved by all authors.

Funding: None; Competing interests: None stated.

1. Sanghvi U, Diwakar KK. Universal screening for congenital hypothyroidism. Indian Pediatr. 2008;45:331-2.

2. Bhatia V. Congenital hypothyroidism is not always permanent: caveats to newborn thyroid screen interpretation. Indian Pediatr. 2010;47:753-54.

3. Wu LL, Sazali BS, Adeep N, Khalid BA. Congenital hypothyroid screening using cord blood TSH. Singapore Med J. 1999;40:23-6.

4. Nascimento ML, Silva PC, Simoni G, Lobo GS, Souza CD. Congenital hypothyroidism screening programme preliminary results. J Pediatric (Rio J).　1997;73:176-9.

5. Ordookhani A, Mirmiran P, Najafi R, Hedayati M, Azizi F. Congenital hypothyroidism in Iran. Indian J Pediatr. 2003;70:625-8.

6. Kaur G, Srivastav J, Jain S, Chawla D, Chavan BS, Atwal R, et al. Preliminary report on neonatal screening for congenital hypothyroidism, congenital adrenal hyperplasia and glucose-6-phosphate dehydrogenase deficiency: a Chandigarh experience. Indian J Pediatr. 2010;77:969-73.

7. Manglik AK, Chatterjee N, Ghosh G. Umbilical cord blood TSH levels in term neonates: a screening tool for congenital hypothyroidism. Indian Pediatr. 2005;42:1029-32.

8. Dilli D, Çzbaº , Acican D, Yamak N, Ertek M, Dilmen U. Establishment and development of a national newborn screening programme for congenital hypothyroidism in Turkey. J Clin Res Pediatr Endocrinol. 2013;5:73-9.