PREDICTION OF POSTPARTUM GRAVES THYROTOXICOSIS BY MEASUREMENT OF THYROID-STIMULATING ANTIBODY IN EARLY-PREGNANCY

OBJECTIVE Autoimmune thyroid diseases often occur after delivery. Howe ver, it has been difficult to predict who will develop Graves' thyroto xicosis after delivery. We tried to establish a systematic method for predicting postpartum onset of Graves' thyrotoxicosis. DESIGN We follo wed up the pregnant women with antithyroid microsomal antibody (MCAb) from early pregnancy to the post-partum period and analysed the relati on between the activities of thyroid stimulating antibodies (TSAb) in early pregnancy and post-partum occurrence of Graves' disease. PATIENT S Seventy-one women with positive MCAb in early pregnancy were studied . They were randomly selected from 262 MCAb-positive subjects found in 3405 consecutive early pregnant women who attended our maternity clin ic during the last ten years. MEASUREMENTS MCAb was measured with a co mmercially available agglutination kit. For 71 MCAb-positive subjects, TSH-binding inhibitory immunoglobulin (TBII) and TSAb were measured i n early pregnancy, and serially until 6 months after delivery for the subjects with either positive TBII or TSAb. Thyroid function and goitr e size were recorded at every observation. RESULTS Among the 71 subjec ts, 7 showed positive TSAb in early pregnancy without any thyroid dysf unction; all 7 developed thyroid dysfunction in the post-partum period . Five of them (70% of TSAb-positive subjects) developed Graves' disea se, two showing persistence and three transiently. None of 64 TSAb-neg ative subjects developed Graves' thyrotoxicosis, though 44 developed v arious types of thyroid dysfunction as a result of postpartum autoimmu ne thyroiditis. CONCLUSION The individuals at high risk of post-partum onset of Graves' thyrotoxicosis can be found early in their pregnancy by the detection of TSAb. Overall occurrence of post-partum Graves' d isease in the general population is estimated above 0.54%, that is, on e in 200 post-partum women may develop Graves' thyrotoxicosis, althoug h thyrotoxicosis may be transient in half of the patients.