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MS WordPerinatologist Corner - C.E.U/C.M.E. Modules
Nausea and Vomiting in Pregnancy
Sponsored by The Indian Health Service Clinical Support Center
6. What about thyroid disease in pregnancy?
While nausea and vomiting is not a common symptom of hyperthyroidism,
it has somehow become routine to order thyroid functions on these women.
Signs of hyperthyroidism
If you have read the Perinatologist Corner on Thyroid Disease in Pregnancy, you will recall that these women, who typically have high human chorionic gonadotrophin (HCG) levels, will frequently have an assay for TSH that often returns very low, suggesting hyperthyroidism. This may occur in up to 20% of pregnant women in whom the newer third generation, ultrasensitive TSH assays are obtained. These women may even have a mildly elevated free T4, but they will be clinically euthyroid, without tremor, tachycardia, hyperreflexia, or the other signs of hyperthyroidism.
Both these biochemical abnormalities will resolve by 18 weeks and anti-thyroid medications should not be started. (They will not help the nausea and vomiting either!) They may cause the fetus, who is totally dependent on its mother’s thyroxine until its own gland becomes functional at about 18 weeks, to become hypothyroid, with the accompanying later intellectual deficits.
Features that distinguish the transient hyperthyroidism of hyperemesis gravidarum from hyperthyroidism of other causes (which in a pregnant woman is most likely to be due to Graves' disease) are the vomiting, absence of goiter and ophthalmopathy, and absence of the common symptoms and signs of hyperthyroidism (heat intolerance, muscle weakness, tremor). In addition, serum free T4 concentrations are only minimally elevated and serum T3 concentrations are not elevated in women with hyperemesis gravidarum, whereas both are usually unequivocally elevated in pregnant women with true hyperthyroidism. Treatment of hyperthyroidism should not be undertaken without clear evidence of a primary thyroid disorder (eg, goiter, elevated free thyroid hormone or elevated TSH receptor antibody levels).
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