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Pregnancy morning sickness caused by thyroid changes.

Pregnancy Morning Sickness Caused By Thyroid Changes

OSAKA, JAPAN: A team of Japanese researchers has found that changes in thyroid function occur during the first trimester of pregnancy that correlate with the severity of early-morning nausea and vomiting known as "morning sickness," but that the changes are no cause for alarm and do not indicate thyroid disease.

For their study, Masao Mori, M.D., and colleagues from Osaka University Medical School measured in 132 healthy women in early pregnancy and in 20 nonpregnant healthy women blood levels of thyroxine (T4), of thyroid-stimulating hormone (TSH), and of the early-pregnancy hormone human chorionic gonadotropin (hCG), which causes the release of a variety of hormones that maintain the pregnancy and is also known to have a thyroid-stimulating effect.

All women were free of clinically detectable forms of thyroid disease. The pregnant women were categorized based on the severity of morning sickness: no symptoms, nausea only, and nausea and vomiting. The researchers found that not only were blood concentrations of T4 significantly greater, and TSH levels significantly lower, in pregnant than in nonpregnant women, higher blood levels of T4 (and hCG) "were especially marked in subjects with nausea and vomiting."

Later in pregnancy, when women no longer had morning sickness, T4 and TSH levels returned to "normal," i.e., that of nonpregnant women. Because the blood concentrations of T4 correlated strongly with levels of hCG (confirming the thyroid-stimulating effects of hCG), and earlier studies showed that women with severe morning sickness including vomiting had higher blood levels of hCG than women who felt well during early pregnancy, the researchers concluded that activation of the thyroid gland by hCG may be the cause of vomiting during early pregnancy. They emphasized that changes in T4 and TSH during early pregnancy are usually normal, do not indicate antityroid drug treatment." necessitate anthyroid drug treatment."
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Publication:Nutrition Health Review
Date:Jun 22, 1989
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