The management of thyrotoxicosis among women who are expected to become pregnant has its own special problems. Since thyrotoxic patients are often troubled with thyroid dysfunction for a long period of time, they sometimes risk a poor outcome of pregnancy. The purpose of this study is to consider the best way of treating thyrotoxic patients of childbearing age.
A retrospective study of 506 pregnancies is presented here. These 506 pregnancies are divided into three groups : first, the 170 patients who became pregnant during antithyroid drug therapy, (D.D.); second, the 125 patients who became pregnant after completing antithyroid drug therapy, (A.D.); and third, the 211 patients who became pregnant after subtotalthyroidectomy, (A.S.).
In D.D. and A.D., patients sometimes became pregnant when they were hyperthyroid. In these cases, the fetal losses were more than 20%. On the other hand, when the patients became pregnant in euthyroid, the fetal losses of each group were 14.1% and 7.4%, respectively. In D.D., 22% of the patients became hyperthyroid during pregnancy, while 10% did in A.D.. There were some cases which became hypothyroid during pregnancy : these were 10% in D.D. and 1.6% in A.D.. 70% in D.D. and 60% in A.D. were relapsed after delivery.
As for the A.S. group, the fetal loss among cases with normal function during pregnancy was 7.8%. In seven pregnancies in A.S., supplemental hormone therapy had started before pregnancy because of hypothyroidism and there was only one fetal loss. Three of the 10 in A.S. who were hypothyroid during pregnancy without receiving thyroid hormone failed to carry their infants alive. In A, S., there were 127 cases in which thyroid function was not examined during pregnancy and fetal loss among them was as high as 26.8% (34 cases), Sixteen of them were found to have overt hypothyroidism or subclinical hypothyroidism judging from a rise in serum TSH after delivery, and were suspected of being hypothyroid during pregnancy.
Of the 422 neonates in this series, 7 had anomalies (1.7%). There was no goitrous neonate. Of the 161 infants whose mothers had taken methimazole in their first trimester, three had anomalies (1.8%) including umbilical hernia and Fallot's tetrad. In these cases, the mothers had received more than 15 mg of methimazole per day.
These results may suggest that if patients become pregnant during drug therapy, their thyroid functions will become unstable during pregnancy more often and they will have a higher percentage of relapses after delivery as compared with those who become pregnant after drug therapy. In addition, it has not been denied that maternal antithyroid drug therapy might have a bad effect on the fetus. Therefore, patients should be recommended to become pregnant after completing drug therapy and should be careful not to become pregnant when they relapse.
As for surgery, relapses occurred infrequently indicating that there is less effect of hyperthyroidism on pregnancy; in addition, there is no need to worry about drug influence on the fetus and relapse after delivery. Since, it takes much time to complete drug therapy, subtotalthyroidectomy may be thus considered to be the best kind of therapy, especially for the patients who are planning to become pregnant in the near future. But in these cases a thyroid function test should sometimes be done after the operation so as not to risk patients being in a hypothyroid state. Appropriate replacement therapy with thyroid hormone should be given, if necessary.
