Thyroid dysfunction is common during pregnancy and can be detected with the help of thyroid function tests.
What is Thyroid?
The hormone that controls the secretion of thyroid hormone is Thyroid-stimulating Hormone (TSH), which is secreted by a small gland in the brain called the pituitary. Thus, if the level of thyroid hormone is low, the pituitary secretes more TSH to stimulate the thyroid. The reverse is the case if the thyroid hormone levels are high.
The condition where thyroid hormone levels are low is referred to as hypothyroidism while the condition where thyroid hormone levels are high is referred to as hyperthyroidism. Hypothyroidism is more common in pregnancy as compared to hyperthyroidism.
Thyroid Problems during Pregnancy:
Hypothyroidism during Pregnancy: Hypothyroidism is more common during pregnancy as compared to hyperthyroidism. If untreated, it can result in goiter in the fetus and even malformations. However, if it is detected at the right time, the condition can be easily treated with thyroid hormone tablets, thus preventing any adverse consequences.
Hyperthyroidism during Pregnancy: Hyperthyroidism can also have serious consequences on the mother as well as the baby if it is untreated. In pregnancy, a drug called propylthiouracil is preferred for its treatment.
Unfortunately, there is no consensus whether thyroid function should be carried out in all pregnant women. However, it is definitely recommended for women who are at a higher risk for developing thyroid disease, which includes all women over the age of 30 years. Tests used to detect thyroid dysfunction in pregnancy are:
TSH: Measurement of TSH levels is a common test done for screening thyroid disease in pregnancy. A high level indicates hypothyroidism, while a low level indicates hyperthyroidism. It should however be remembered that both the upper and lower limits of TSH are lesser during pregnancy as compared to the non-pregnant state. The levels also vary according to the trimester.
Other tests are usually done if the TSH levels are abnormal. These include:
Free T4 Levels: The T4 hormone is present in two forms, the free form and bound to protein. Since the protein levels in the blood increase during pregnancy, the total amount of the T4 hormone is higher. It is therefore necessary to measure the free T4 level, which gives a more accurate picture of the thyroid status during pregnancy.
Thyroid Antibodies: The presence of thyroid peroxidase antibodies along with slightly high TSH levels and normal free T4 levels can result in complications like miscarriage. These cases therefore should be treated with thyroid hormone.
Free T3 Levels: The level of this hormone is also altered in hyper and hypothyroidism, though this test is not commonly done in pregnant patients.
1. Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and Postpartum