Evaluation of the Fetal Brain in Maternal Hypothyroidism and Thyroid Autoantibody Positivity: A Prospective Case-Control Study

<b>Background/Objectives</b>: Maternal thyroid function plays a crucial role in fetal brain development, yet the potential impact of maternal hypothyroidism and thyroid autoimmunity on fetal intracranial structures remains inadequately explored. To investigate the impact of maternal hypothyroidism and thyroid autoimmunity on fetal intracranial structures, focusing on potential alterations in critical brain parameters during mid-gestation. <b>Methods</b>: This prospective case-control study included pregnant women between 18 and 24 weeks of gestation. Participants were divided into three groups: hypothyroidism and antibodies (Ab) group, hypothyroidism and Ab(-) group, and the control group. Ultrasonographic measurements of fetal intracranial structures such as the posterior lateral ventricle (PLV), cavum septum pellucidi (CSP), cisterna magna (CM), thalamus, and transcerebellar diameter (TCD) were recorded and compared. <b>Results</b>: A total of 153 pregnant women were evaluated (n = 52 in the hypothyroidism and Ab(+) group, n = 51 in the hypothyroidism and Ab(-) group, and n = 50 in the control group). Although most of the biometric parameters were similar across the groups, the hypothyroidism and Ab(+) group exhibited significantly lower PLV and thalamus measurements compared to the control group (<i>p</i> < 0.05). Additionally, there was a notable difference in the BMI among the groups, with hypothyroid participants (with or without antibodies) showing higher rates of being overweight or obese. <b>Conclusions</b>: Maternal hypothyroidism and the presence of thyroid autoantibodies may be associated with subtle changes in fetal brain structures during the mid-gestation period, particularly in the thalamus and PLV.