Combined detection of α-fetoprotein and free β-human chorionic gonadotropin in screening for trisomy 21 and management of cases in the moderate risk value range.

Down syndrome is the most common cause of prenatal chromosomal abnormalities, and prenatal serum screening is an effective method for decreasing the birth prevalence of children with Down syndrome. The aim of the present study was to observe the effect of duplex screening and investigate the treatment of cases under specific conditions. The medians of free β-human chorionic gonadotropin (HCG) and α-fetoprotein (AFP) were calculated and compared with those embedded in the 2T software. The detection and false-positive rates were analyzed under different conditions, and the distribution of Down syndrome cases was investigated in different risk ranges. Finally, suitable recommendations for further diagnostic investigation were provided according to the status of each individual. The medians of free β-HCG and AFP were found to differ from the corresponding medians embedded in the 2T software (P<0.01), and on the basis of a 5% false-positive rate, the detection rate would increase from 63.6 to 67.8% when compared with medians embedded in the 2T software, indicating we should establish our own medians of free β-HCG and AFP. In addition, residual cases (risk value <1/300) with relevant Down syndrome indications mainly concentrated at risk values between 1/1,000 and 1/300, and partial residual screening cases were verified through diverse methods. These findings indicated that different laboratories should establish their own medians; furthermore, what is classed as moderate risk is extremely important in screening for Down syndrome and reasonable recommendations may be offered under different conditions.