From pregnancy preparation to pregnancy, why is thyroid screening so important?

Author: Yang Zhaojun, Chief Physician of China-Japan Friendship Hospital

Reviewer: Wu Xueyan, Chief Physician, Peking Union Medical College Hospital

With the adjustment of fertility policies and the development of society, more and more families choose to have a second or even third child. However, as they age, many women face higher health risks during pregnancy.

Among them, the thyroid gland is an important organ of the human endocrine system, and its normal function is directly related to the health of pregnant women and fetuses.

1. Types and screening of thyroid diseases during pregnancy

Thyroid diseases during pregnancy mainly include hypothyroidism (abbreviated as hypothyroidism), hyperthyroidism (abbreviated as hyperthyroidism), and thyroid nodules. Among them, hypothyroidism has attracted much attention due to its prevalence and potential serious consequences. The incidence of hypothyroidism is high in pregnant women, especially in older pregnant women. Therefore, for pregnant women with a family history of thyroid disease, previous thyroid abnormalities, positive thyroid antibodies, unexplained miscarriage or premature birth, it is recommended to undergo thyroid disease screening within the first three months of pregnancy.

Screening mainly includes two parts: morphological examination and hormone level determination. Morphological examination mainly uses thyroid ultrasound to observe whether the thyroid gland has nodules or enlargement. Hormone level determination is to draw blood samples to test thyroid stimulating hormone (TSH), free thyroxine (FT3, FT4) and thyroid antibodies to assess thyroid function. The combination of these two tests can more comprehensively assess the thyroid health of pregnant women.

Figure 1 Original copyright image, no permission to reprint

2. Changes and monitoring of thyroid hormone levels during pregnancy

During pregnancy, hormone levels in the pregnant woman's body change significantly to accommodate the growth and development of the fetus.

For the thyroid gland, this change is equally obvious. In early pregnancy, due to the sharp rise in human chorionic gonadotropin (HCG), the thyroid gland will be stimulated to secrete more thyroid hormones, resulting in a decrease in TSH levels and even a brief hyperthyroidism-like performance. However, as pregnancy progresses, TSH levels will gradually return to the normal range, but will still be lower than the non-pregnant state. At the same time, T4 levels show a gradual upward trend throughout pregnancy, reaching up to about twice the non-pregnant level.

Therefore, pregnant women should regularly monitor their thyroid hormone levels during pregnancy to promptly detect and treat possible thyroid dysfunction. For high-risk pregnant women, early thyroid screening and close monitoring of hormone level changes are particularly important. Once abnormalities are found, they should seek medical attention in a timely manner and receive intervention treatment under the guidance of a doctor.

3. Impact of thyroid disease on maternal and infant health

Thyroid disease is potentially harmful to both pregnant women and fetuses. Mild thyroid dysfunction may not have a significant impact, but severe hyperthyroidism or hypothyroidism may lead to a series of adverse consequences.

For example, hyperthyroidism can restrict fetal development and cause low birth weight; it also increases the risk of fetal growth retardation, miscarriage, and premature birth. In addition, TRAb (thyroid hormone receptor antibodies) produced in patients with hyperthyroidism can enter the fetus through the placenta and cause neonatal hyperthyroidism. For pregnant women, thyroid disease may cause symptoms such as weight loss and palpitations, and increase the risk of complications such as heart failure, preeclampsia, and hypertension.

Figure 2 Original copyright image, no permission to reprint

For female hyperthyroidism patients who are not yet pregnant, they can consider pregnancy after their thyroid function is well controlled and stabilized at a certain level. However, they still need to pay close attention to changes in thyroid function before and during pregnancy, and adjust the treatment plan and drug dosage under the guidance of a doctor.

Hypothyroidism during pregnancy can also increase the risk of adverse pregnancy outcomes, such as premature birth, low birth weight, fetal death, miscarriage, etc.; it can also have adverse effects on the fetus's neurological and intellectual development.