Understand hyperthyroidism during pregnancy and protect your baby’s health!

Author: Xiao Jianzhong, Chief Physician of Beijing Tsinghua Chang Gung Hospital affiliated to Tsinghua University

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

We know that after pregnancy, due to the increase in estrogen and progesterone levels and the increase in basal metabolic rate, pregnant women are prone to symptoms such as sweating and body heat. These are usually normal physiological conditions and do not require special treatment.

However, everyone should also pay attention, because hyperthyroidism can easily cause symptoms such as palpitations and sweating, so pregnant women must seek medical attention in time if they experience any discomfort. Do not take it for granted that it is normal and avoid delaying treatment.

If you feel anxious, hot, and sweat a lot during pregnancy, you should actively check the five thyroid function tests. Among the five thyroid function tests, the most important indicator is TSH (thyroid-stimulating hormone). Current studies have found that its upper limit of normal value is about 4mIU/L, and the lower limit is about 0.2mIU/L.

However, due to different hospitals, different measurement methods, and different measurement equipment used in laboratories, the reference range of this value is also different. In addition, its level is also different in different stages of pregnancy, early, mid, and late.

For example, in early pregnancy, due to the interference of human chorionic gonadotropin (HCG) on TSH, TSH is generally low. In the middle and late stages, the range of low TSH values ​​will increase. For example, in the early stage, that is, the first 12 weeks of pregnancy, the normal value of TSH is 0.1-4mIU/L, in the middle stage, the normal value of TSH is 0.2-4mIU/L, and in the late stage, the normal value of TSH is 0.3-4mIU/L. Therefore, the reference range of normal TSH values ​​is not the same in different periods.

TSH is secreted by the pituitary gland, and the hormones secreted by the thyroid gland are mainly T3 and T4. T4 is a very important indicator. Because pregnancy causes an increase in thyroid binding protein, which leads to a physiological increase in total T4 (TT4), we mainly rely on TSH and free T4 (FT4) to determine whether it is hyperthyroidism during pregnancy.

Hyperthyroidism during pregnancy can only be diagnosed when a pregnant woman shows obvious symptoms such as heat intolerance, palpitations, sweating, and increased heart rate, and at the same time, TSH decreases and FT4 increases.

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If you develop hyperthyroidism during pregnancy and the indicators are relatively high, there are risks to both the pregnant woman and the fetus, so you must actively seek treatment.

For example, the commonly used drug for treating hyperthyroidism is called methimazole, which has an impact on the development of the fetus in early pregnancy and may cause problems such as fetal scalp defects. If it is replaced with propylthiouracil tablets, the risk will be relatively smaller.

There are two very important viewpoints in the treatment of hyperthyroidism during pregnancy: the first is to let the index be higher rather than take too large a dose of medicine; the second is not to give drugs to treat hyperthyroidism and hypothyroidism at the same time.

Because in the treatment of hyperthyroidism, some doctors like to give drugs for hyperthyroidism and hypothyroidism at the same time, but this treatment is not recommended during pregnancy. Because this treatment means that pregnant mothers have to take higher doses of drugs for hyperthyroidism, and these drugs can pass through the placenta to affect the fetus, affect the fetus's thyroid gland, and cause fetal hypothyroidism.

Some pregnant mothers worry that the drugs for treating hyperthyroidism will affect the fetus, so they stop taking the drugs privately. This is not recommended because if the hyperthyroidism is severe, miscarriage or premature birth is more likely to occur after stopping the drugs.

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Medically speaking, taking medicine does have certain risks, but the risks are not so great that you cannot have the baby and need to have an abortion. Therefore, close monitoring during medication, observing whether the fetus is growing and developing normally, and adjusting treatment in a timely manner are important ways to prevent problems.

In addition, pregnant women with hyperthyroidism also have some dietary precautions:

First, for most patients with hyperthyroidism, hyperthyroidism is a state of high metabolism, so the food eaten will become an ineffective metabolism. It cannot produce energy, and symptoms such as fever and sweating are likely to occur. Therefore, it is very important to ensure the calorie supply of food at this time.

Second, the demand for vitamins, especially B vitamins, will increase, so providing adequate vitamins is also very important.

Third, because iodine is the raw material for synthesizing thyroid hormone, hyperthyroidism generally requires appropriate iodine restriction. But during pregnancy, about 8 weeks later, the fetus's thyroid gland will develop and need raw materials to synthesize its own thyroid hormone, so we do not recommend iodine restriction at this time. As for iodine-containing foods, a normal diet is sufficient. Don't eat too much, and don't deliberately restrict it. This may be a better attitude.

Of course, another way is to determine the nutritional status of iodine by measuring urine iodine. There are requirements for urine iodine in pregnant women, for example, a level of 150-250 μg/L per day is appropriate. If the iodine is too low, you need to supplement it. If the iodine is too high, you need to control the intake of iodine-containing foods.