Midtrimester maternal serum free beta-human chorionic gonadotropin levels: normal reference values for Taiwanese women.

BACKGROUND: The purpose of this study was to establish normative median values for maternal serum free beta-human chorionic gonadotropin (beta-hCG) during the second trimester of pregnant Taiwanese women. MATERIALS AND METHODS: We collected the data of midtrimester serum free beta-hCG concentration levels from 15,132 normal Taiwanese singleton pregnancies between 14 and 22 weeks' gestation. The maternal age on the day of delivery and maternal weight at the time of sampling were recorded in all cases. The relationship between gestational days and multiple of the median (MoM) levels of serum markers was analyzed using nonlinear regression methods. RESULTS: The median values of free beta-hCG in pregnant Taiwanese women were higher than those of pregnant white women. The log10 standard deviation distribution of free beta-hCG MoM values in the study population was 0.275 with a log10 mean of 0.0097. There were 1.81% of pregnancies with free beta-hCG levels less than 0.3 MoM and 11.33% with levels less than 0.5 MoM; 12.91% had serum levels greater than 2.0 MoM and 5.29% had serum levels greater than 3.0 MoM. CONCLUSION: Because of differences in race and methodology, any laboratory intended to provide determination of free beta-hCG for Down syndrome screening should establish its own normal reference values.