Definition
About 2.5% of pregnant women are affected by hypothyroidism. This means that the thyroid gland does not produce enough thyroid hormones (T3, T4). Hypothyroidism can either have occurred before pregnancy or develop only as a result of the increased demands during pregnancy. Since an undersupply of maternal thyroid hormones carries many risks for the unborn child, it should be diagnosed as early as possible and treated accordingly. However, hypothyroidism in pregnancy can be treated well and does not have any negative effects on the child.
Causes
In hypothyroidism, the thyroid gland produces less hormones than the body needs for mother and child during pregnancy. This undersupply slows down the metabolism and as a result the unborn child can suffer mental and physical deficits. There are various causes for an underactive thyroid during pregnancy.
The hypothyroidism can either have existed before the pregnancy or develop during it. During pregnancy, the need for thyroid hormones increases by about 50% because the baby has to be supplied by the mother. A healthy thyroid gland can easily compensate for this increased need, whereas hypothyroid pregnant women cannot cover the need and need thyroid hormone substitution.
A hypofunction that develops only during pregnancy can completely disappear after birth. Pre-existing hypothyroidism is often caused by a chronic inflammation of the thyroid gland (Hashimoto’s thyroiditis), which is triggered by the body’s own immune system. Hypothyroidism can also be induced by medication or can develop after an overdose of thyrostatic drugs that inhibit thyroid function.
In some cases hypothyroidism is caused by benign or malignant tumors in the thyroid gland. After surgical removal of the thyroid gland after a carcinoma, there is also a deficiency of thyroid hormones. A hypofunction due to iodine deficiency is rather rare in our latitudes, since iodine is added to table salt as a precautionary measure.
Diagnosis
An underactive thyroid during pregnancy can be clearly diagnosed by the doctor on the basis of a blood count with hormone determination. The size of the thyroid gland can be determined by means of palpation and ultrasound diagnostics, but an assessment of its function is only possible on the basis of blood values. If the thyroid gland is underfunctioning, the TSH values are increased, whereas the amount of free thyroxine (T4) in the blood is reduced. If hypothyroidism has been diagnosed, thyroid hormone substitution and regular blood checks during pregnancy are urgently required to prevent damage to the foetus.