Improved contingent screening strategy increased trisomy 21 detection rate in the second trimester.

PURPOSE: This study aimed to establish suitable threshold values for biochemical indicators in low-risk pregnant women who underwent second trimester screening and design strategies for consecutive prenatal testing to increase trisomy 21 detection.

METHODS

This study examined singleton pregnant women who underwent double, triple, or quadruple screening in the second trimester over six years. To obtain adequate detection efficiency for low-risk pregnancies, threshold values for serum biochemical indicators were established, and a cost-effectiveness assessment of the improved contingent screening strategy was conducted.

RESULTS

Participants were included in serum double- (n = 88,550), triple- (n = 29,991), and quadruple-screening (n = 15,004) groups. Threshold values were defined as having a free beta subunit of human chorionic gonadotropin (free β-hCG) multiple of the median (MoM) ≥ 2.50, alpha-fetoprotein (AFP) MoM ≤ 0.50, or unconjugated estriol (uE3) MoM ≤ 0.70 for low risk. Low-risk pregnancies, comprising 1.35% (988/73,183), 4.45% (1,171/26,286), and 11.91% (1,559/13,085) of the double-, triple-, and quadruple-screening groups, respectively, underwent further non-invasive prenatal screening. In the double-, triple-, and quadruple-screening groups, we detected 11.76% (2/17), 40.00% (2/5), and 66.67% (2/3) of trisomy 21 cases with false negative results, respectively, with the overall detection rates of 85.00% (85/100), 90.63% (29/32), and 95.24% (20/21), respectively, and decreased ratio of overall costs of 5.26%, 16.63%, and 24.36%, respectively.

CONCLUSION

Utilizing threshold values of AFP, free β-hCG, and uE3 to trigger further non-invasive prenatal screening may increase trisomy 21 detection in pregnancies deemed low risk in the second trimester while reducing the overall costs of screening strategies.