Association between second trimester maternal hypothyroidism and congenital heart diseases in fetuses: a retrospective study

Aim: This study aimed to investigate the association between second-trimester maternal hypothyroidism and congenital heart diseases (CHDs) in fetuses. Material and Methods: This retrospective study was conducted at Obstetrics and Pediatrics Training and Research Hospital between June 2022 and December 2024. The patient group comprised mothers of children diagnosed with major CHDs, while the control group included mothers of children without CHDs or with minor anomalies not requiring intervention. Maternal thyroid status was determined by second-trimester TSH levels: >4.0 mIU/mL was classified as hypothyroid, while 0.2–4.0 mIU/mL was considered euthyroid. Statistical analyses, including ROC analysis, regression analysis, Chi-square test, Fisher's exact test, and Mann-Whitney U test, were performed using SPSS 25, with p < 0.05 considered significant. Results: The median TSH level was significantly higher in the CHD group compared to controls (p = 0.002). Logistic regression analysis revealed that each unit increase in maternal TSH levels increased the risk of fetal CHD by 1.47 times (95% CI: 1.212–1.792, p < 0.001). ROC analysis determined an optimal TSH cutoff of 1.795 mIU/mL (AUC = 0.627; sensitivity: 59.6%, specificity: 59.4%). While differences in CHD subgroups were observed, including conotruncal and valvular defects, these did not reach statistical significance (p > 0.05). Conclusion: The study suggests a potential association between maternal hypothyroidism and fetal CHD.