What is gestational transient thyrotoxicosis?

Gestational transient thyrotoxicosis (GTT) is a temporary condition of an overactive thyroid in pregnant women caused by high levels of one of the main pregnancy hormones (HCG). In this condition, women will have raised FT4 and low TSH levels in early pregnancy, and have had no symptoms before pregnancy.

How can it be distinguished from Graves’ disease?

Although women may experience some symptoms in common with hyperthyroidism (intolerance to heat, tremors, anxiety, palpitations etc.), they are unlikely to be positive for the thyroid antibodies linked to hyperthyroidism (TRAb). Their FT3 will usually be normal or mildly raised, unlike in Graves’ where it will be raised. The FT3/FT4 ratio will also be normal and TSH will usually normalise by the 3^rd trimester.

Women are also unlikely to have any of the other signs or symptoms associated with a true underlying overactive thyroid e.g. a goitre, eye symptoms, weight loss before pregnancy or a personal or family history of thyroid disease with this condition. If they have symptoms of Hyperemesis Gravidarum (nausea/vomiting), it is more likely to be GTT.

What are the risks?

GTT does not put pregnancy at higher risk and usually clears up by itself by the end of the first or early second trimester.

Does it require treatment?

It does not usually require antithyroid drug treatment, only symptomatic and supportive management e.g. beta blockers for rapid heart rate.

Read the RCOG Green-top guideline on the Management of Thyroid Disorders in Pregnancy