Thyroid hormone binding in early pregnancy and the risk of spontaneous abortion

Serum thyroxine (T4), free thyroxine (FT4) and thyroxine binding globulin (TBG) were measured at 6, 8, 10, 12, 14 and 16 weeks menstrual age (MA) in 32 pregnant females, who had been selected for a high risk of spontaneous abortion on account of previous abortion (18 cases) or ovulation induction (14 cases). Eight of these subjects experienced a spontaneous abortion occurring between 8 and 20 weeks. The other women, who carried to term, served as controls. In the abortion group, mean pre-abortion TBG and T4 levels were lower than in the control group from the 6th week on. In spite of this, the way T4 changes with TBG was very similar in both groups. No detectable change or difference with respect to control values were observed for FT4. These observations are taken as evidence against impaired maternal thyroid function playing a role in the unsuccessful outcome of pregnancy. Decreased TBG was detected on the average at 5.2 (range 0-13) weeks before abortion. Diagnostic sensitivity and positive predictive value were estimated as about 70 and 80%, respectively, for the high-risk group, indicating that serum TBG might only play a minor role as a predictor of the outcome of pregnancy.