British zyxwvutsrqpo Journal zyxwvutsrq of zyxwvuts Obstetrics and G~~naecology May 1987, Vol. 94. zyxwvutsrq pp. 483-484 Transient hyperthyroidism in pregnancy. Case report R. K. H. CHIN, T. T. H. LAO, C. S. COCKRAM, R. SWAMINATHAN, N. S. PANESAR Case report A 35-year-old Chinese housewife was admitted to hospital with a 10-day history of severe vomit- ing in her third pregnancy. There was no other significant family, medical, or past obstetric history except that both her elder sister and her niece had a history of hyperthyroidism. On admission she wasmarkedly dehydrated and ket- onuric. Ultrasound scanning revealed a single, viable fetus at 8 weeks gestation. Her symptoms initially improved with intravenous fluid replace- ment and anti-emetic therapy but deteriorated 1 week later so much that she requested termina- tion of pregnancy. At that time a sleeping tachy- cardia of 130/min was present. The thyroid gland was diffusely enlarged with a loud bruit. There were no additional features to suggest Graves’ disease. Investigation revealed markedly ele- vated plasma total and free thyroxine (T4) and triiodothyronine (T3) concentrations (Table l), but the red blood cell zinc concentration was not decreased. Thyroid antibodies were absent. The serum beta human chorionic gonadotrophin (B-hCG) was high (Table 1). Because of the short history and early gestation it was decided to observe her progress and antithyroid treatment was therefore withheld. As her symptoms sub- sequently improved spontaneously, termination of pregnancy was not considered justified and she went home 3 weeks later. By 13 weeks, her symp- toms had largely subsided and the began to gain weight steadily. Her subsequent course of preg- nancy was uneventful. Serial measurements of Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong Department of Obstetrics and Gynaecology R. K. H. CHIN T. T. H. LAO Department of Medicine C. S. COCKRAM Department of Chemical Pathology R. SWAMINATFIAN N. S. PANESAR Correspondence: Dr R. K. zyxwvuts €3. Chin zyxwvu 1’4 and T3 concentrations showed a steady fall towards normal in parallel with a fall in B-hCG, despite the expected rise in the serum T4-binding globulin with advancing gestation. She had an uncomplicated labour at term and was delivered of a 3.2 kg healthy baby girl. Discussion Our patient displayed an uncommon and recently recognized complication of early preg- nancy-namely transient hyperthyroidism which has also been called pregnancy-induced thy- rotoxicosis (Dozeman et al. 1983; Jeffcoate zy & Bain 1985). The degree of elevation of total and free T4 and T3 concentrations, as well as the clini- cal features, confirmed that true hyperthyroid- ism occurred. The transient nature of the hyperthyroidism was supported by a normal erythrocyte zinc con- centration. Most of the zinc in erythrocytes is present in the enzyme carbonic anhydrase of which there are two isoenzymes B and C. The isoenzyme B and associated zinc concentration is much reduced in hyperthyroid patients (Auton et al. 1976). However, this abnormality will appear at first only in young red cells and a measurable fall in concentration will only occur as these cells graduallyreplace those which were present in the circulation before the onset of hyperthyroidism. Thus changes in erythrocyte zinc concentration will take time to occur (Swaminathan ef al. 1976) and the presence of a normal concentration pro- vides additional strong support for the transient nature of the hyperthyroidism in this patient and confirms that she had been euthyroid in the weeks immediately preceding the onset of the hyperemesis. The role of hCG in hyperemesis gravidarum has been disputed. It may be causal since hyper- emesis gravidarum is more common in multiple pregnancies and molar pregnancies, conditions associated with a raisedconcentrationof hCG. A positive correlation between hCG con- centrations and women who have nausea and vomiting during early pregnancy has been 483