Abstract
Background: The thyroid status of mothers and neonates has a profound impact on neonatal brain development. Hypothyroidism at birth is one of the preventable causes of mental retardation in children. Low birth weight is an important cause of neonatal morbidity and mortality. Many factors responsible for low birth weight can be fetal or maternal. Evidence-based interventions could save many newborns. For this, the knowledge has to be transformed into practice. Method: This study was performed at a medical college and tertiary care hospital in western India's Thane district of Maharashtra. Eligible female participants were those who have enrolled in the hospital over 5 months from February through June 2021. All statistical analyses were performed using Mystat statistical software version 12.0 or Statistical Package of Social Sciences version 20.0 for Windows (IBM Corp, Armonk, NY). The normality of the data distribution was determined using the Kolmogorov-Smirnov test.
Result: Maternal TSH and thyroxin are more than that of cord blood counterparts, while cord blood T3 levels were found to be more than maternal T3. Maternal TSH has a positive correlation with the birth weight of neonates. It shows a significant negative correlation with the birth weight of cord blood T3 (r = -0.563) and Thyroxin (r = -0.510), respectively. The higher the maternal thyroxin and T3, the lower the birth weight. Conclusion: Present study shows the effect of thyroid status of mother and fetus both has an association with neonatal birth weight. More detailed analysis with sample collection as per trimester is required to know more about the impact of various confounding factors which have an impact on birth weight. Maternal TSH rather than thyroxin is a better predictor of neonatal birth weight.

Key words: Birth weight, T3, T4, TSH