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J Obstet Gynaecol Res. 2012 Apr;38(4):686-91. doi: 10.1111/j.1447-0756.2011.01769.x. Epub 2012 Mar 2.

Different median levels of serum triple markers in the second trimester of pregnancy in a Thai Ethnic Group.

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Department of Obstetrics and Gynecology, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand.



The aim of the present study was to establish Thai-specific reference ranges of triple markers for fetal Down syndrome as a function of gestational age as well as weight correction models and to compare the false positive rates when using Thai-specific model relative to Caucasian-specific model.


A total of 993 normal Thai pregnant women were determined for mid-trimester serum levels of alpha-fetoprotein (AFP), free-beta human chorionic gonadotropin (hCG), and unconjugated estriol (uE3), using DefiaXpress system (Perkin Elmer, Waltham, MA, USA).


The models of Thai-specific medians for AFP, b-hCG, and uE3, as well as the models for weight correction were derived and the normal reference ranges were constructed. The best fitted equation for AFP, b-hCG and uE3 are as follows: predicted median = 2.675 × 10((0.153 × GA in week)), r = 0.979; 10((-0.717 + 57.487/GA in week)) , r = 0.991; and 10((5.678-69.346/GA) (in) (week)), r = 0.99, respectively. The models were properly applied to another group of 302 Thai women, signifying that they were reliable models. The weight-adjusted gestation-specific medians derived from Caucasian models were significantly higher than those based on Thai models and the false positive rate could be reduced from 10 to 7.1% when Thai models were applied.


Thai reference ranges of triple screen markers as a function of gestational age as well as weight correction models have been established. The Caucasian reference range, even after weight correction, gives a positive rate that is much higher than that it should be, strongly suggesting the need for ethnicity-specific medians.

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