Retrospective study derives gestational age and postnatal age specific TSH cutoffs for preterm infants

This retrospective cohort analysis examined thyroid-stimulating hormone (TSH) reference ranges and screening cutoffs in preterm infants who underwent neonatal blood screening tests (NBST) between October 2017 and December 2022. The stated rationale was that the same TSH cutoffs are currently applied to term and preterm infants, and the authors sought to determine whether preterm-specific thresholds are warranted.

Newborns were classified by gestational age (GA), birth weight (BW), and small-for-gestational-age (SGA) status. Within each category, the 2.5th, 5th, 50th, 95th, and 97.5th percentiles of TSH levels were calculated, with the 97.5th percentile designated as the screening cutoff. Reference thresholds were then derived for different postnatal age (PNA) periods.

Cut-off values differed across GA, BW, and SGA subgroups. During the first four weeks after birth, the 97.5th percentile TSH level followed a sequential pattern of initial decline, subsequent rise, and final decrease, peaking at 7.38 μIU/mL in the third postnatal week. SGA infants had significantly higher TSH levels, though the specific p-value was truncated in the available abstract text.

Because the abstract does not report overall sample size, specific subgroup counts, term-infant comparator data, funding, or conflict-of-interest disclosures, the magnitude and generalizability of these thresholds cannot be fully judged from the available information. No safety or adverse-event data are applicable given the screening-focused design.

For clinicians, these findings support the principle that preterm TSH screening interpretation may require GA-, BW-, and PNA-stratified thresholds rather than a single term-infant cutoff, with particular attention to SGA infants and to the third postnatal week when the upper reference bound appears highest.