Overtreatment of Transient Maternal Hyperthyroidism Resulting in Fetal Goiter.

* Abbreviations: EXIT: : ex utero intrapartum treatment hCG: : human chorionic gonadotropin PTU: : propylthiouracil T3: : triiodothyronine T4: : thyroxine TSH: : thyroid-stimulating hormone TSI: : thyroid-stimulating immunoglobulin A 25-year-old gravida 1 para 0 pregnant woman was referred to our fetal center at 33 weeks and 1 day of gestation after an incidental fetal neck mass was identified on ultrasonography. Her pregnancy was complicated by weight loss, hair loss, and palpitations in early gestation as well as persistent nausea and vomiting. This prompted an evaluation that was notable for a low thyroid-stimulating hormone (TSH) level (0.06 mIU/L; normal range: 0.27–4.20 mIU/L) and an elevated free thyroxine (T4) level (2.11 ng/dL [27.16 pmol/L]; normal range: 0.86–1.76 ng/dL [11.0–22.6 pmol/L]). The thyroid antibody panel, including thyroid peroxidase antibody and thyroglobulin antibody, was normal. She was diagnosed with hyperthyroidism and treated with propylthiouracil (PTU) at a dose of 150 mg twice a day. Both the TSH and free T4 concentrations normalized on this regimen. A third-trimester fetal growth scan showed a new finding of a fetal neck mass consistent with a fetal goiter, prompting referral to our center for further evaluation. Early detection and expedited management of fetal goiter is important for optimal infant outcomes. Referral to a tertiary center is recommended if there is a concern for a large fetal goiter. When a pregnant woman is referred to the Texas Children’s Hospital Fetal Center because of a fetal goiter, we perform fetal imaging to determine the risk of postnatal airway obstruction and, if this risk is present, establish a plan for management in the delivery room. We also assess for other abnormalities because many fetuses with a goiter also have other findings, such as a pericardial effusion or a hyperextended neck. If there is an esophageal obstruction because of the mechanical effect of the goiter, this may limit fetal swallowing of the amniotic fluid. In turn, this may lead to polyhydramnios and a small stomach size seen on …