TSH in pregnancy – norms and fluctuations. How to interpret the results?

TSH levels in pregnancy are not constant all the time. It varies depending on the advancement of the trimester. It’s easy to miss symptoms of thyroid dysfunction by not testing for TSH, since many of them (like increased body weight or constipation) are attributed to the physiology of pregnancy and considered quite normal.

TSH norms in pregnancy

Pregnancy testing of TSH, a hormone secreted by the pituitary gland, is used to assess the quality of the thyroid gland. It allows to confirm the presence of disorders of its functioning and indicate their nature. TSH, or thyrotropin, during the fetal life of the child is responsible for the proper development of the central nervous system and skeletal system, which is why early and frequent diagnosis for TSH levels during pregnancy is so important. Particularly dangerous is too high levels of hormones secreted by the thyroid gland, i.e. hypothyroidism of the gland, which can interfere with the development of the fetus. 

However, the TSH concentration in pregnancy is not a constant value and varies from trimester to trimester. This is a natural and quite normal phenomenon. The physiological low level of TSH in pregnancy is at ca. 10-12weeks of pregnancy. TSH norms in the first trimester of pregnancy in Poland  are in the range of 0.1-2.5 mIU/l. In the second trimester, they range from 0.2-3 mIU/l. In contrast, 7 months after conception, the thyrotropin status stabilizes and reaches a level of 0.3-3 mIU/l, which should persist until termination. 

TSH test in pregnancy is performed based on a blood sample. When test results are above normal, that is, their value is too low or too high, drug treatment is undertaken to regulate hormone levels. TSH checks are also being intensified. TSH testing is particularly recommended for pregnant women burdened with chronic thyroid disorders, as well as women who develop alarming symptoms suggesting deviations from normal in the level of the hormone.

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Low TSH in pregnancy – effects

Normal TSH during pregnancy can be disrupted by a variety of factors. Low TSH levels indicate hyperthyroidism, which is diagnosed less frequently than hypothyroidism resulting from too high levels of the hormone. It is also associated with fewer complications. The effects of low thyrotropin are mainly weight loss, weakness, lethargy, tachycardia, excessive sweating and irritability. In women who are burdened with hyperthyroidism even before pregnancy, the discomfort may worsen especially in the first trimester. However, in all pregnant women struggling with low TSH, symptoms usually resolve spontaneously after delivery. The most common complication arising from hyperthyroidism is hypertension.

High TSH in pregnancy

Elevated TSH in pregnancy carries more dangerous consequences than too low a level of the hormone. Hypothyroidism is characterized by an ambiguous course. Drowsiness, weight gain, edema, dry skin, constipation or weakness appear. Symptoms of this type are most often identified with the physiology of pregnancy, so they can be underestimated, with the danger of complications. High TSH levels in pregnancy primarily threaten anemia and hypertension. It also poses a risk of placental detachment, premature labor and even hemorrhage in the postpartum period. Babies born with untreated hypothyroidism, or elevated maternal TSH during pregnancy, are often distinguished by low birth weight and even developmental abnormalities later in life.

See also: Hashimoto’s and pregnancy