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.
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