American journal of perinatology
-
Fetal tachycardia caused by the transplacental passage of thyroid stimulating immunoglobulin is well established, but very little information exists regarding the fetal heart rate appearance of this form of tachycardia. Two cases of fetal tachycardia are described in pregnancies complicated by fetal thyrotoxicosis where maternal thyroid history was unknown at the time of testing. ⋯ The tracings were essentially normal except for the baseline rate. When reviewing the differential for fetal tachycardia presenting in the antenatal period, this pattern is unique to fetal thyrotoxicosis, especially if the mother is afebrile and there is no history of medication usage that could explain this presentation.