Pregnant women go through a number of physiological changes that affect the thyroid gland. In particular, pregnancy brings on higher levels of hormones, such as estrogen, which can alter the levels of thyroid hormones in the blood.
In most cases, the thyroid usually continues to function properly. But the hormonal stresses of pregnancy can bring on either hyperthyroidism or hypothyroidism. Thyroid problems can be difficult to diagnose during pregnancy because the symptoms of thyroid dysfunction are often similar to the normal symptoms of pregnancy (fatigue, weight gain, changes in mood or sleeping patterns). Pregnant women should be monitored for potential thyroid problems.