ObjectiveTo observe and analyze thyroxine levels in children with retinopathy of prematurity (ROP) and its effect on severe ROP. MethodsA retrospective clinical study. From January 2022 to December 2023, a total of 64 premature infants with severe ROP (ROP group), hospitalized in the Children's Hospital Affiliated to Zhengzhou University and with a gestational age ≤32 weeks, were included. According to a 1:2 ratio, 128 premature infants without ROP, matched for sex and gestational age, were selected as the control group. Thyroid function tests were performed 7 to 14 d after birth. The levels of thyroid-stimulating hormone, triiodothyronine, free triiodothyronine, thyroxine (T4), and free T4 (FT4) were compared and observed between the two groups. The quantitative data between groups were compared by independent samples t-test or Mann-Whitney U test; the count data were compared by χ2 test. Logistic regression was used to analyze the correlation between various variables and the occurrence of severe ROP. The predictive efficacy of the differential indicators was assessed by receiver operating characteristic (ROC) curve. ResultsCompared with the control group, T4 and FT4 levels were significantly lower in children in the ROP group, and the difference was statistically significant (t=2.572, 2.704; P=0.011, 0.008). The results of univariate logistic regression analysis showed that the Apgar scores at 1 and 5 minutes, as well as sepsis, T4, FT4, and bronchopulmonary dysplasia (BPD), were significantly associated with the occurrence of severe ROP (P ＜ 0.05). The results of multivariate logistic regression analysis indicated that FT4 and BPD are independent risk factors for the occurrence of severe ROP (P ＜ 0.05). The ROC curve analysis showed a sensitivity of 80.9% and a specificity of 43.3% for T4. The abnormal threshold was 98.4 nmol/L. ConclusionsThe T4 and FT4 level of children with severe ROP are lower than that of children without ROP in the early postnatal period. The T4 and FT4 level in the early postnatal period may have a certain correlation with the occurrence of severe ROP.