Prevalence of gestational thyrotoxicosis in Asian women evaluated in the 8th to 14th weeks of pregnancy: correlations with total and free beta human chorionic gonadotrophin

Objectives The Prevalence of gestational transient thyrotoxicosis (GTT) in Europeans evaluated during the 8th to 14th weeks of pregnancy is 2-3%. Howe ver, there is evidence that GTT may be more common in some Asian population s. The aims of this study were to evaluate the prevalence of thyroid hormon e abnormalities in Asian women in their 8th to 14th weeks of pregnancy usin g highly sensitive free T4 and TSH assays and to correlate these with total and free beta -hCG levels. Design and patients One hundred and eighty-four consecutive unselected Asia n (Singaporean) pregnant women seen at ante-natal clinics for the first tim e and who were in their 8th to 14th weeks of pregnancy were tested. Measurements Serum free T4, free T3, TSH, total beta -hCG and free beta -HC G levels were measured on the Vitros ECi system (Johnson & Johnson Ortho-Cl inical Diagnostics, Amersham, UK) which employs chemiluminescent immunochem ical technology. This free T4 assay Is free of biases related to serum bind ing capacity. The TSH assay used was a third generation assay. Thyrotrophin -receptor antibody (TRAb) levels were measured using LUMItest TRAK (BRAHMS Diagnostica, Berlin, Germany). Results Two subjects (1.1%) were found to have Graves' disease. Elevated fr ee T4, free T3, total T3 and suppressed TSH were seen in 14.8%, 3.3%, 26.4% and 33.0% of the remaining 182 pregnant women, respectively. Total and fre e beta -hCG correlated negatively with TSH (r=-0.30, P<0.0001 and r=-0.29, P<0.0001, respectively), positively with fT4 (r=0.283, P<0.001 and r=0.253, P<0.001) and fT3 (r=0.273, P<0.001 and r=0.204, P<0.01). 11.0% of cases ha d gestational thyrotoxicosis (GT) defined as elevated free T4 (>19.1 pmol/l ), suppressed TSH (<0.36 mIU/I) and TRAb levels within the reference interv al (0-0.9 U/I). The prevalence of GT was significantly higher in patients t ested at 8-11 weeks compared to those evaluated at 12-14 weeks (14.4% vs. 4 .7%, P<0.05). Total beta -hCG (P=0.0002), free beta -hCG (P<0.0001) and fre e T4 (P=0.02) levels were higher and TSH levels (P=0.01) lower in patients tested at 8-11 weeks. Significant positive correlations between both total and free <beta>-hCG with free T4 were seen at 8-11 weeks but not in patient s tested at 12 weeks or later. TT3 levels were similar in the two groups. Conclusions Using sensitive assays, the prevalence of gestational thyrotoxi cosis In Asian women was found to be 11.0% and was significantly higher in subjects at 8-11 weeks of gestation than at 12-14 weeks. The positive corre lation between hCG and free T4 seen in patients tested at 8-11 weeks was ab sent in patients tested at later stages of the first trimester. Future stud ies investigating the entity of gestational thyrotoxicosis, at least in Asi an patients, should focus on patients at earlier stages of gestation than c urrently practised.