Thyroid Research Thyroid Research Archive Pregnancy

Women with hyperemesis gravidarum may have transient hyperthyroidism

(November 2002)

The background of the study. Pregnant women have transient increases in thyroid secretion from approximately 6 to 16 weeks of gestation, caused by the thyroid-stimulating action of the placental hormone chorionic gonadotropin. These changes are magnified in women with hyperemesis gravidarum, and some may be considered to have hyperthyroidism caused by Graves' disease (and to need antithyroid-drug therapy). This case study was done to define the clinical and biochemical characteristics and course of women with hyperemesis gravidarum who had high serum thyroid hormone concentrations.

How the study was done. The study subjects were women with hyperemesis gravidarum, defined as persistent vomiting beginning before 13 weeks of gestation that was so severe that the woman needed to be hospitalized to be given intravenous fluids for more than three days or on more than one occasion. The women were evaluated by clinical examination; measurements of serum thyrotropin (TSH), free thyroxine (T4), and electrolytes; and tests of liver function.

The results of the study. Among 78 women hospitalized for treatment of hyperemesis gravidarum, 39 had transient hyperthyroidism. Their mean age was 30 years; the mean duration of gestation was 9 weeks; and 35 had singleton pregnancies and 4 had twin pregnancies. Twenty-two women (56 percent) lost >5 percent of their prepregnancy weight. None had symptoms or signs of hyperthyroidism or Graves' disease. At first admission, 26 of the 39 women (67 percent) had low serum sodium concentrations, and 23 (59 percent) had low serum potassium concentrations.

The peak mean serum free T4 concentration in these 39 women was 3.1 ng/dl (40 pmol/L) (upper limit of normal, 2.0 ng/dl [26 pmol/L]) at 9 weeks of gestation, after which the values fell progressively; all the women had normal serum free T4 concentrations by 15 weeks. Their initial serum TSH concentrations were low, but increased thereafter in all women. The ratio of female to male infants was 2.6:1.

The conclusions of the study. Women with hyperemesis gravidarum may have transient hyperthyroidism, which subsides during the second trimester. Thereafter, their pregnancies and deliveries are normal.

The original article. Tan JY, Loh KC, Yeo GS, Chee YC. Transient hyperthyroidism of hyperemesis gravidarum. BJOG 2002;109:683-8.