Determinants of thyroid function in neonates at birth

Abstract

Introduction: Thyroid function test is commonly done in neonatal period to evaluate thyroid status. Interpretation of T4 and Thyroid stimulating hormone (TSH) values in the immediate post natal period is difficult due to wide physiological variation in their levels and potential influence of multiple factors. There is paucity of regarding thyroid function tests and the determinants.

Aims: To assess the average level of T4 and TSH and to identify the impact of gestational age, birth weight, gender and mode of delivery on thyroid function in newborn. This is a prospective study conducted in neonatal care unit of tertiary hospital. Total of 108 neonates are enrolled in the study. Studied population were divided into groups based on sex, gestational age, birth weight and mode of delivery.

Methods and Material: Venous sample is obtained at the age of 72-120 hours of life from a peripheral vein. The sample is sent for T4 and TSH levels estimation.

Results: Mean T4 of 7.0±4 in Preterm is significantly lower than 10.1±5.6 in term neonates (p<.o1). Positive significant correlation of T4 with gestational age was observed ((r=0•68 and P<0•01). TSH negatively correlated significantly with gestational age (r=−0•34 and P<0•01). Significant difference in mean T4 and TSH was noted in low birth weight (LBW) and in neonates weighing >2.5kg. Low birth weight (VLBW) also showed low levels of T4 which was significantly lower compared to low birth weight babies. TSH levels showed no difference between LBW and VLBW neonates. Gender and mode of delivery had no significant impact on T4 and TSH levels.

Conclusions: Interpretation of T4 and TSH levels should be done with caution. In the postnatal period normative gestational age and birth weight specific data should be available before interpretation of thyroid levels. This will avoid unnecessary reinvestigations and follow-up.