ESPE Abstracts

Background: Increase in incidence of congenital hypothyroidism (CH) is explained by detection of transient CH (TCH), previously commonly underdiagnosed, due to neonatal screening programs. Current guidelines recommend that treatment be started immediately after diagnosis and that hypothalamic-pituitary-thyroid (HPT) axis be reevaluated after 3 years of age. We aimed to identify the factors associated with TCH, such as the perinatal history or L-thyroxine (LT4) dose per weight.

Methods: Clinical, anthropometric, laboratory and radiological data of 145 children with CH visiting the pediatric endocrinologic clinic between January, 2018 and March, 2023 were retrospectively analyzed. We compared the gestational age (GA), birth weight, maternal history, NST level at screening, initial serum TSH, fT4 level and LT4 dose per weight at every 6 months between TCH and permanent CH (PCH) group. Continuous data were analyzed using the student t-test and categorical variables were analyzed using the χ2 test. To identify the association between covariates and TCH, univariate and multivariate Cox proportional hazards models were performed.

Results: 77 (53.1%) children were classified in the TCH and 68 (46.9%) in the PCH. GA and birth weight between TCH and PCH showed statistical difference, 36.2 weeks versus 38.5 (P<0.001) and 2.64 kg versus 3.02 kg (P=0.008), respectively. TCH group (n=21/77, 27.3%) had more maternal thyroid disease than PCH group (n=6/68, 8.8%). Preterm birth, low birth weight, maternal thyroid disease, positive for routine test, low TSH level at screening and low L-Thyroxine (LT4) dose at subsequent age were associated with TCH in the univariate analysis. In the Cox multivariate analysis, preterm birth (adjusted Hr= 2.554, CI_95% [1.593-4.095], P<0.001) and low LT4 dose at 30 months of age (adjusted Hr= -0.799, CI_95% [0.362-0.559], P<0.001) remained statistically associated with TCH. LT4 dose at 30 months age of 3.24 µg/kg/day could suggest TCH (sensitivity, 66.2%; specificity, 66.2%).

Conclusion: Our study showed that preterm birth and low LT4 dose at 30 months of age was highly suggestive of TCH.