Diagnostic Utility of Cord Thyroid-Stimulating Hormone (TSH) in Congenital Hypothyroidism and Its Association With Perinatal Factors: A Study From a Tertiary Referral Centre in Hyderabad, India.

Introduction Congenital hypothyroidism (CH) is one of the most common, easily treatable, causes of long-term neurodevelopmental complications in children. The prevalence of CH in India is much higher compared to other countries. Although developed countries have well-established neonatal screening programs, a uniform nationwide screening program at birth is still not established in India. Cord blood thyroid-stimulating hormone (TSH) screening is crucial in diagnosing congenital hypothyroidism even with advancements in expanded newborn screening programs. The aim of this study was to determine the prevalence of elevated cord blood TSH levels and factors associated with it among newborns and to analyze the false positive rates of elevated cord blood TSH levels among the study population and factors associated with it. Methods This retrospective cross-sectional study was conducted among 51,251 live newborn babies born at Fernandez Hospital, Hyderabad, India, over a period of five years from January 2019 to December 2023. The data of all the mothers and newborns was retrieved from medical records and details of maternal age, parity, co-morbidities, mode of delivery, gestational age of the newborn at delivery, gender, number of babies, APGAR score, and birth weight were obtained. As per hospital policy, 5 ml of cord blood sample of all newborn babies was collected from the umbilical cord at the time of birth. Samples were analysed for cord TSH batchwise by the enzyme-linked immunosorbent assay (ELISA) method. As per the manufacturer, the normal biological reference intervals are <20 uIU/mL. All the cord TSH values > 20 uIU/ mL were considered abnormal and advised a repeat serum TSH test within 14 days of life. Cord TSH values that were higher than the biological reference range after retesting were considered positive for CH. All the initial and repeat results were retrieved from the neonatal digital database. Results Out of 51,251 live newborn babies, 71 (0.14%) were confirmed with a diagnosis of congenital hypothyroidism. The prevalence of CH in our study population was 1.4 per 1000 live births. Anaemia was found to be a statistically significant predictor of true positive cases (p<0.05). In our study, while evaluating risk factors for elevated cord TSH levels, we found that the babies born by vaginal delivery had higher cord TSH levels than babies born by lower segment caesarean section (LSCS) (p<0.001). The other variables considered in the study which include maternal age, BMI, parity of mother, gender of the baby, birth weight, gestation age and APGAR score were not statistically significant for CH. Conclusion The prevalence of congenital hypothyroidism was 1.4 in 1000 in our study. Mode of delivery and maternal anaemia had an impact on elevated cord TSH levels. These factors should be considered while interpreting cord TSH values. Cord TSH testing is an effective screening tool for CH. It helps in the early detection of thyroid dysfunction in newborns, enabling timely intervention and treatment to prevent developmental delays and other complications. This study presents evidence supporting the inclusion of cord blood TSH as a predictive factor in CH screening programs.