A Study On The Association Of Human Chorionic Gonadotropin (hCG) With Hyperthyroidism During The First Trimester Of Pregnancy

ObjectiveTo investigate the prevalence of gestational transient thyrotoxicosis (GTT) and itsproportion hyperthyroidism during the first trimester of pregnancy. To approach therelationship between serum hCG level and thyroid function during the first thrimesterof pregnancy.MethodsA epidemiologic study in Shenyang was performed. We obtain 534 healthyearlypregnant (during the first trimester of pregnancy) women who have no personaland family history of thyroid diseases, no drug history(eg, estrogen) of anythingresulting change in thyroid function or no goiter. Questions about thyroid disorderswere asked. The thyroid function, thyroid autoantibodies (TPOAb, TRAb) and serumhCG were performed in the subjects.Results1. The total prevalence of hyperthyroidism is 9.75%, in which clinical andsubclinical are 4.49% and 5.26% separately. There are 42 patients with GTT. So thelatter account for 80.77%in the former. The prevalence of the latter is 7.86% (clinical is3.37% and subclinical is 4.49%). There isn't any significance between the prevalenceof clinical and subclinical hyperthyroidism for both the former and latter. Within theGTT, the prevalence of clinical hyperthyroidism in 12 gestational week (GW) is higherthan that in 6GW (P＜0.05); the total prevalence in 8～10GW and 12GW is significantlyhigher than that in 6GW (P=0.005,P=0.009); besides, the prevalence of the clinical andsubclinical is similar in earlypregnancy. 2. The median of serum hCG in 6GW is the lowest (P=0.000). The medians ofserum TSH degrade gradually (6,8～10,12GW) (P＜0.01). The two show a mirror imagerelationship. During 6～10GW, serum FT₄ and FT₃ maintain a steady level; in 12GW,slightly drops FT₄ and rises FT₃ (P=0.000).3. For the patients of clinical and subclinical GTT and the normal control, themedians of serum TSH degrade, and those of serum hCG, FT₄, FT₃ upgrade. Within the18 patients of clinical GTT, 16 patients have a normal FT₄ and elevated FT₃ level, andthe proportion is 88.89%. It is thus evidence that elevated FT₃ is the serologicalcharacteristic of clinical GTT during the first trimester of pregnancy.4. According to serum hCG level, 477 pregnant women (negtive TPOAb, TRAb)are divided into five groups (≤20,000 IU/L,～≤50,000 IU/L,～≤80,000 IU/L,～≤110,000IU/L and＞110,000IU/L). The medians of serum TSH for every group degrade gradually.The correlation analysis shows that serum hCG and TSH have a negative correlation(r=-0.402, P=0.000), serum hCG and FT₃ have a positive correlation (r=0.163,P=0.000), while serum hCG and FT₄ have no correlation.ConclusionDuring the first trimester of pregnancy, the prevalence of GTT is 7.86%, which isthe most common cause of hyperthyroidism (80.77%); serum hCG and TSH have anegative correlation, serum hCG and FT₃ have a positive correlation, while serum hCGand FT₄ have no correlation; during the first trimester, the serological characteristic ofclinical GTT is a elevation of serum FT₃.