RISK OF SUBCLINICAL HYPOTHYROIDISM IN PREGNANT-WOMEN WITH ASYMPTOMATIC AUTOIMMUNE THYROID-DISORDERS

A prospective study was undertaken in 87 healthy pregnant women with t hyroid antibodies and normal thyroid function at initial presentation [asymptomatic autoimmune thyroid disorders (AITD)]. The aims of the st udy were to assess whether women with AITD constitute a group at risk of developing subclinical hypothyroidism during pregnancy, and whether a mild thyroid function impairment may be associated with obstetrical repercussions. The women investigated were selected among a cohort of 1660 consecutive pregnancies on the basis of 1) no previous history o f thyroid disease, 2) euthyroidism at initial presentation, and 3) pos itive thyroglobulin antibodies and/or thyroid peroxidase antibodies (T PO-Ab). Women with AITD had a basal TSH value significantly higher, al beit still normal, in the first trimester (1.6 us. 0.9 mU/L; P < 0.001 ) than that in women with healthy pregnancies used as controls. Despit e a 60% average reduction in TPO-Ab titers during gestation, serum TSH remained higher in women with AITD than in controls throughout gestat ion: at delivery, 40% of the cases had serum TSH levels above 3 mU/L, and 16% had serum TSH levels above 4 mU/L. A TRH test carried out in t he days after parturition showed an exaggerated response in 50% of the cases. Furthermore, free T-4 concentrations were in the range of hypo thyroid values in 42% of the women. Obstetrical repercussions were obs erved, namely increased rates of spontaneous miscarriage and premature deliveries.In conclusion, women with asymptomatic AITD who are euthyr oid in early pregnancy carry a significant risk of developing hypothyr oidism progressively during gestation, despite a marked reduction in a ntibody titers. Hypothyroidism results from the reduced ability of the gland to adjust to the changes in thyroidal economy associated with p regnancy. At the individual level, progression to subclinical hypothyr oidism was broadly predictable on the basis of serum TSH levels and TP O-Ab titers in the first trimester. Hence, these parameters provide us eful markers to identify women who carry a higher risk, allowing for a close monitoring of thyroid function during pregnancy and the adminis tration of L-T-4 in specific cases. Taken together with the known inci dences of postpartum thyroiditis and hypothyroidism in women with AITD , the present observations in our opinion justify systematic screening of thyroid autoimmunity during pregnancy.