Median levels of serum biomarkers of fetal Down syndrome detected during the first trimester among pregnant Thai women

Abstract

Objective: To develop Thai-specific medians of serum pregnancy-associated plasma protein A (PAPP-A) and free β-human chorionic gonadotropin (hCG) levels during the first trimester of pregnancy and to compare these values to a Caucasian-specific model for the detection of fetal Down syndrome.

Methods: Serum concentrations of PAPP-A and free β-hCG were measured during the first trimester in a group of 2339 Thai women undergoing normal singleton pregnancies.

Results: Thai reference ranges of PAPP-A and free β-hCG were established by gestational age (70-98 days). The equation of best fit for PAPP-A was: predicted median PAPP-A level=28.767 - 0.781×(gestational age in days)+0.006×(gestational age in days)(2); r=0.986. The equation of best fit for free β-hCG was: predicted median free β-hCG level=465.332×10((-0.024×gestational age in days)); r=0.881. Weight-corrected models were also derived for each biomarker. The Thai-specific reference ranges gave higher positive screening rates than the Caucasian-specific model, even after weight correction (5.1% versus 4.0%). The Thai-specific models were validated in an independent group of 302 pregnant women.

Conclusion: Ethnic group-specific medians for PAPP-A and free β-hCG should be incorporated during first-trimester screening for fetal Down syndrome.