About 1 in 500 women have hyperthyroidism during pregnancy. In some, it is a preexisting condition; in others, the condition will develop during the course of the pregnancy. It can be difficult to diagnose because the pregnancy often "masks" it; that is, some of the symptoms may be attributed to the pregnancy itself rather than to hyperthyroidism.
Hyperthyroidism may affect a woman's ability to become pregnant.
The most common cause of hyperthyroidism in pregnancy is Graves' disease.
Symptoms generally will be worse in the first half of the pregnancy, will lessen during the second half, and most likely will recur after the baby is born.
You should continue with your normal anti-thyroid medication during your pregnancy as prescribed by your doctor.
Most pregnant women and their babies will not experience significant problems if the hyperthyroidism is mild to moderate. If properly treated the pregnancy can be expected to progress normally.
Women with severe or uncontrolled hyperthyroidism have an increase risk of infection, iron deficiency (anemia), and high blood pressure accompanied by too much protein in the urine (a potentially dangerous condition called pre-eclampsia).
If a woman has severe hyperthyroidism, her baby has a chance of having hyperthyroidism as well. There is a risk to the outcome of the pregnancy, having a small baby or a premature birth.
Fortunately, most women who have hyperthyroidism in pregnancy can be successfully treated with medication. The anti-thyroid drug Propylthiouracil is commonly prescribed and can be safely used during pregnancy. It may take up to a month on medication for the symptoms to resolve. Radioactive iodine cannot be used during pregnancy. Rarely, if the symptoms and thyroid hormone levels cannot be controlled, surgery needs to be considered to remove the thyroid gland.
Hyperthyroidism does not affect labor and delivery. However, thyroid storm can develop which can be life threatening. The symptoms are an exaggeration of the normal hyperthyroid symptoms with a very fast heart rate, tremors, nervousness, altered consciousness, nausea, vomiting, diarrhea, and an extremely high fever. This will require intensive care treatment to try normalizing the very high thyroid hormone levels and keeping the patient cool.
Following delivery, anti-thyroid treatment must continue. Although both the anti-thyroid drugs Propylthiouracil and methimazole do pass into the breast milk, both can be used safely in breast-feeding women. You should discuss this with your physician.
Your baby will be thoroughly checked to be sure he or she is well with no evidence of thyroid problems. Most babies born to hyperthyroid mothers whose hyperthyroidism has been well controlled during pregnancy are normal healthy babies.