I am an expecting mother with a history of thyotoxicosis. I have been on PTU during pregnancy. My doctor recommends that I stop medication four weeks before delivery. Why is that? What is the adverse impact if I continue with medication until child birth? (Translation from Chinese)

Thyrotoxicosis is normally progressively improved during pregnancy and therefore most patients can be off medication before delivery. When medications are stopped, patient will be guided by blood tests on the thyroid function as well as clinical examination. In general most patients can be off treatment for the last three months of gestation. But blood tests are also needed at interval after delivery as hyperthyroidism can recur, and treatment may be needed again. If the dose of PTU is more than 200 mg a day in the last three months, there is risk of fetal goitre. But a lower dose can be used if necessary to maintain the patient in the euthyroid state.