Serum levels of intact human chorionic gonadotropin (HCG) and its free a and β subunits, in relation to maternal thyroid stimulation during normal pregnancy

Abstract

The main objective of the present study was to present additional evidence of the potentially important thyrotropic role of hCG to regulate the maternal thyroid gland during normal pregnancy. Sequential determinations (first and last trimesters) of intact hCG, free alpha and beta-hCG subunits concentrations (using monoclonal IRMAs), and assessment of parameters of thyroid function and thyroid volume were carried out in 62 pregnant women who exhibited during the first trimester of gestation low TSH levels (< or = 0.20 mU/L), and compared to 276 pregnant women with normal TSH levels. The prevalence of having low serum TSH represented 18% of all pregnancies, with almost one half of cases who transiently had undetectable TSH levels. Lowering of TSH was associated with high hCG levels, and occurred primarily during the first trimester. About 10% of women with low TSH presented transient gestational thyrotoxicosis, frequently associated with vomiting. In comparison to control subjects, women with a suppressed serum TSH had significantly and markedly higher intact hCG and free beta-hCG subunit concentrations. The results suggest that TSH reduction may result from a relative oversecretion of both intact hCG and free beta-hCG subunits, compatible with three hypotheses: a) transient overexpression of the beta-hCG gene, leading to enhanced production of hCG heterodimer; b) increased glycosylation of circulating hCG, with in turn a prolonged half life; c) larger syncytiotrophoblast mass with increased hCG production.(ABSTRACT TRUNCATED AT 250 WORDS)

Transient hyperthyroidism of hyperemesis gravidarum

“…This is consistent with other studies which have reported that resolution of hyperthyroidism occurs within a time frame of 1-10 weeks 1 . Glinoer et al 7 showed that hCG remained abnormally elevated for several weeks during the second trimester and that normalisation of free T4 levels paralleled the decline in hCG, supporting its role in the pathogenesis of transient hyperthyroidism of hyperemesis gravidarum. Unfortunately, our study did not look at hCG levels.…”

“…In a study that looked at TSH blunting in a large group of pregnant women during the three trimesters, 18% of women in the first trimester had transiently subnormal TSH levels (as well as higher mean hCG levels) with almost half being undetectable (<0.05 mU/L). Eleven percent of the women with undetectable TSH levels also had elevated free T4 levels 7 . Isolated TSH suppression therefore forms one end of this spectrum followed by the additional finding of elevated free T4 levels and finally, transient hyperthyroidism of hyperemesis gravidarum.…”

Autoimmune Thyroid Disease in Pregnancy: A Review

“…Nevertheless, 10%-20% of pregnant women may have serum TSH levels that are low compared to the range of TSH found in nonpregnant women (either subnormal or fully suppressed) without coexisting thyrotoxic symptoms. 25,71 When TSH is very low, a trend in the serum T 4 and T 3 serum levels may help in differentiating transient GTT from a truly thyrotoxic state. Therefore, more than just biochemistry is necessary for full confidence in the diagnosis.…”

Management of subclinical hypothyroidism in pregnancy: are we too simplistic?

“…Placental production of human chorionic gonadotrophin (hCG) and a rise in oestrogen production that increases binding proteins, namely thyroxinebinding globulin affect free TH levels. TSH dips according to most but not all studies within the first trimester, whereas free TH concentrations decrease, albeit very slightly, mainly during the latter part of pregnancy (10,11,14,15,16,17,18,19). These observed alterations are not only due to pathophysiological changes but are, at least in part, due to methodological issues.…”