Increased serum reverse triiodothyronine in patients with hyperemesis gravidarum

Thyroid function and pituitary responsiveness to TRH were studied in patients with hyperemesis gravidarum. Serum T3 and T4 concentrations were normal. Serum TBG levels in hyperemesis were normal for gestation, and the T4:TBG ratio was in the euthyroid range. In all patients a normal TSH response to TRH was found. Mean serum rT3 concentration was increased by 31% as compared to a control group of normal pregnant women (P less than 0.001). The data suggest that in patients with hyperemesis gravidarum there is: (a) normal function of the thyroid gland and pituitary-thyroid axis, (b) an enhanced peripheral conversion of T4 to rT3.