Background: Identifying congenital hypothyroidism through newborn screening (NBS) is higher among moderate-to-late preterm (MLPT) infants. Currently, the same thyroid-stimulating hormone (TSH) cutoffs are used for term and preterm infants. TSH reference ranges for MLPT infants are not currently available.
Objective: To determine TSH reference ranges for MLPT infants.
Methods: We analyzed 10,987 TSH levels on NBS samples performed on 8499 MLPT infants born between 32 and 36 weeks gestation.
Results: TSH median, 5th, 25th, 75th, 95th, and 99th percentiles were defined from day 1 until day 14 of life. TSH levels gradually decreased after birth and reached a plateau around day 6.
Conclusion: Using a state-wide cohort, we constructed TSH reference charts from day 1 until day 14 for MLPT infants. Relationship between age-adjusted TSH percentiles and long-term neurodevelopmental outcomes should be determined in future studies to define optimal TSH cutoffs for MLPT infants.