Physiological and pathological aspects of the effect of human chorionic gonadotropin on the thyroid

Abstract

Human chorionic gonadotropin (hCG) is a glycoprotein hormone that has structural similarity to TSH. At the time of the peak hCG levels in normal pregnancy, serum TSH levels fall and bear a mirror image to the hCG peak. This reduction in TSH suggests that hCG causes an increased secretion of T4 and T3.Women with hyperemisis gravidarum often have high hCG levels that cause transient hyperthyroidsm. In the vast majority of such patients, there will be spontaneous remission of the increased thyroid function when the vomiting stops in several weeks. When there are clinical features of hyperthyroidism, it is be reasonable to treat with antithyroid drugs or a betaadrenergic blocker, but treatment is rarely required beyond 22 weeks of gestation.Hyperthyroidism or increased thyroid function has been reported in many patients with trophoblastic tumors, either hydatiditform mole or choriocarcinoma. The diagnosis of hydatidiform mole is made by ultrasonography that shows a 'snowstorm' appearance without a fetus. Hydatidiform moles secrete large amounts of hCG proportional to the mass of the tumor. The development of hyperthyroidism requires hCG levels of . 200 U/ml that are sustained for several weeks. Removal of the mole cures the hyperthyroidism. There have been many case reports of hyperthyroidism in women with choriocarcinoma and high hCG levels. The principal therapy is chemotherapy, usually given at a specialized center. With effective chemotherapy, longterm survival exceeds 95%.A unique family with recurrent gestational hyperthyroidism associated with hyperemesis gravidarum was found to have a mutation in the extracellular domain of the TSH receptor that made it responsive to normal levels of hCG.Key words: human chorionic gonadotropin; thyrotropin; pregnancy; hyperemesis gravidarum; hydatidiform mole; choriocarcinoma; mutant thyroid-stimulating hormone receptor.

Hyponatremia associated coma due to pituitary apoplexy in early pregnancy: a case report

“…The interpretation of the remaining pituitary axis at admission and during follow-up was challenging: The thyroid function tests at admission were consistent with the physiologic findings in early pregnancy, reflecting the thyrotropic effects of rising human chorionic gonadotropin (b-HCG) concentration in the first trimester [6,7].Thus, the development of secondary hypothyroidism was masked until the sudden decline of b-HCG because of abortion ( Figure 3). …”

Thyroglobulin level at week 16 of pregnancy is superior to urinary iodine concentration in revealing preconceptual and first trimester iodine supply

“…During pregnancy, the secretory activity of the thyroid gland increases to meet the higher demand for thyroid hormones (Moleti, Trimarchi, & Vermiglio, 2014); this reaches a plateau by week 16. Ending by the end of the first trimester, high human chorionic gonadotropin (hCG) concentration has a transient thyrotropic effect (Hershman, 2004), which may further interfere with the causal relationship between iodine intake and serum Tg concentration. The hCG concentration was a significant predictor for Tg in a group of iodine deficient pregnant women (Koukkou, Ilias, Mamalis, Adonakis, & Markou, 2016).…”

Paraneoplastic hyperthyroidism

“…Some patients with germ cell tumours and high HCG levels develop hyperthyroidism while others do not. One explanation is that there are different forms of circulating HCG molecules (eg, regarding glycosylation), some of which have higher thyrotropic bioactivity, another is that different TSH receptors exist, some of which are potentially hypersensitive to HCG 5. Mutant TSH receptors have been described as a cause of gestational hyperthyroidism 6…”