Screening for Delayed Thyroid Stimulation Hormone Rise and Atypical Congenital Hypothyroidism in Infants Born Very Preterm and Very Low Birth Weight Infants.

OBJECTIVE: To determine among infants born very preterm (VPT) or with very low birth weight (VLBW) the incidence of alterations in thyroid function and associated co-morbidities; the incidence of atypical congenital hypothyroidism (CH) requiring thyroxine therapy; and 3) reference ranges for re-screening at one month of age.

STUDY DESIGN: A retrospective review of infants born VPT or with VLBW and admitted to UCI Medical Center between 1/1/2012 and 12/31/2020. Repeat thyroid screening was obtained at 1 month of life (+ 10 days). Infants with TSH >5 μIU/mL or FT4 <0.8 ng/dL underwent follow-up testing and endocrinology consultation. Initial newborn screening (NBS) and repeat thyroid screening data were collected via chart review. Demographic data and short-term outcomes were abstracted from the California Perinatal Quality Care Collaborative database.

RESULTS: 430 patients were included. 64 out of 429 patients (14.9%) had TSH >5 μIU/mL and 20 of 421 patients (4.8%) had FT4 <0.8 ng/dL. Logistic regression analysis identified small for gestational age (p = 0.044), patent ductus arteriosus (p = 0.013), and late-onset sepsis (p = 0.026) as risk factors associated with delayed TSH rise. Atypical CH requiring treatment through neonatal intensive care unit (NICU) discharge was diagnosed in 6 patients (incidence of 1.4%); none were identified by NBS. The 90th percentile TSH for extremely low birth weight (ELBW) infants (<1000 g) was 7.2 μIU/mL, and the 95th percentile for those with birth weight of 1000-1500g was 6.1 μIU/ml; using these cutoff values identified all infants diagnosed with atypical CH with 100% sensitivity and 90 to 95% specificity. ConclusionAbnormal thyroid function is common in preterm infants. Those infants, including some with atypical CH, are missed by NBS. We recommend repeat thyroid screening with TSH at one month of age in infants born VPT or VLBW infants to identify CH that may require therapy.