Maternal hypothyroidism outcomes on fetal cardiac function

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Maternal hypothyroidism is associated with cardiac remodeling and systolic, diastolic functional alterations in fetuses, according to a recent study published in The Journal of Maternal-Fetal & Neonatal Medicine.

Maternal and fetal thyroid function are closely linked during pregnancy, when increases in thyroid volume, the level of thyroid hormones, and the thyroid autoimmune state occur. Thyroid hormones affect the functions of nervous, endocrine, cardiovascular, and reproductive systems, along with regulating carbohydrate, protein, and fat metabolism.

Women of childbearing age often experience thyroid diseases, such as hypothyroidism, which can lead to increased risks of preterm birth, miscarriage, gestational hypertension, placental abruption, and intrauterine growth restriction. However, the effects of hypothyroidism during pregnancy on fetal cardiovascular structure and function are unclear.

Investigators conducted a study to examine how maternal hypothyroidism impacts fetal cardiovascular structure and function. An experimental group comprised of 59 singleton fetuses with maternal hypothyroidism, while a control group comprised of 74 normal singleton fetuses. Recruitment occurred from November 2018 to November 2019.

Hypothyroidism was defined as maternal serum thyroid stimulating hormone TSH over 4mIU/L and free thyroxine (FT4) within or below the reference level. Exclusion criteria included poor fetal echocardiographic images, fetal congenital cardiovascular disease or other abnormality, other pregnancy complications, and exit during testing.

Along with TSH and FT4 tests, data on age, height, weight, gestational age, maternal history, and medical therapy data with levothyroxine (LT4) were collected. A GE Voluson E10 ultrasonic system with a 2.0–5.0 MHz probe was used to conduct fetal echocardiographic testing.Fetal cardiac and extracardiac abnormalities were determined using routine prenatal ultrasound.

Maternal age, gestational age, number of gestations, and maternal height and weight did not differ between the 2 groups. The experimental group was treated with an average 52.2 ± 34.5 μg dose of LT4 per day.

After treatment, pregnant women had TSH levels under 2.5 mU/L. No individual in the control group needed LT4 for treatment. In the study group, echogenic intracardiac focus was reported in 11 of 59 fetuses, compared to 5 of 74 in the control group. 

The study group also saw reduced thickness of the left ventricular (LV) free wall and interventricular septum, along with significantly lower and right ventricular (RV) fractional shortening (FS). However, cardiothoracic ratio, RV free wall thickness, and LV FS did not significantly differ between the 2 groups.

Certain pulmonary velocities were lower in the study group than the control group, and others were higher. A higher LV Tei index was also seen in the study group.

These results indicated cardiac remodeling and overall function alterations in fetuses with maternal hypothyroidism. Investigators recommended routinely monitoring thyroxine levels during pregnancy to prevent cardiac outcomes in offspring.

Reference

Zhang Y, Zhang L, Zhao W, et al. Cardiac structural and functional remodeling in the fetuses associated with maternal hypothyroidism during pregnancy. The Journal of Maternal-Fetal & Neonatal Medicine. 2023;36(1). doi:10.1080/14767058.2023.2203796