Graves’ disease may present initially during the first trimester or
may be exacerbated during this time in a woman known to have
the disorder. In addition to the classic symptoms associated with
hyperthyroidism, inadequately treated maternal hyperthyroidism
can result in early labor and a serious complication known as
pre-eclampsia. Additionally, women with active Graves’ disease
during pregnancy are at higher risk of developing very severe hyperthyroidism
known as thyroid storm. Graves’ disease often improves
during the third trimester of pregnancy and may worsen
during the post partum period.
The risks to the baby from Graves’ disease are due to one of three
possible mechanisms:
1) Uncontrolled maternal hyperthyroidism: Uncontrolled maternal
hyperthyroidism has been associated with fetal tachycardia
(fast heart rate), small for gestational age babies, prematurity,
stillbirths and possibly congenital malformations.This is
another reason why it is important to treat hyperthyroidism in
the mother.
2) Extremely high levels of thyroid stimulating immunogloblulins
(TSI): Graves’ disease is an autoimmune disorder caused by the
production of antibodies that stimulate thyroid gland referred to
as thyroid stimulating immunoglobulins (TSI). These antibodies
do cross the placenta and can interact with the baby’s thyroid.
Although uncommon (2-5% of cases of Graves’ disease in
pregnancy), high levels of maternal TSI’s, have been known
to cause fetal or neonatal hyperthyroidism. Fortunately, this
typically only occurs when the mother’s TSI levels are very high
(many times above normal). Measuring TSI in the mother with
Graves’ disease is often done in the third trimester.