Abstract
The thyroid hormone triiodothyronine (T3) can be used as an augmentation therapy for depression. This case involves a patient who had been initiated on liothyronine (L-T3) for this purpose and subsequently became pregnant. The exogenous T3 affected maternal thyroid hormone production, including suppression of her thyroxine (T4) levels. In pregnancy, maternal T4 is important for fetal neurodevelopment. Accordingly, use of exogenous T3 for adjunct treatment of depression in pregnant patients or those planning pregnancy requires careful laboratory monitoring of thyroid function tests. In this case, L-T3 was discontinued and the patient was eventually started on levothyroxine (L-T4) and went on to have an uneventful pregnancy.