Second-tier non-invasive prenatal screening for Down syndrome in a public obstetric unit: the first 12 months Abstract

Horace HC CHEUNG, Lai-Yin TONG, William WK TO
Department of Obstetrics and Gynaecology, United Christian Hospital

Objective: To review the uptake rate of non-invasive prenatal testing (NIPT) in the first 12 months of implementation in the obstetric unit of United Christian Hospital.
Methods: Between December 2019 and November 2020, women with a fetal Down syndrome (DS) risk ratio of ≥1:250 after first-trimester DS screening (using maternal serum markers and nuchal translucency thickness on ultrasonography) or second-trimester DS screening (using maternal serum markers) were offered free-of-charge second-tier NIPT or invasive testing. Results of NIPT and invasive testing and pregnancy outcome of these women were reviewed. Characteristics of those opting for NIPT versus invasive testing were compared. Univariate and logistic regression analyses were used to determine significant factors associated with opting for NIPT.
Results: During the study period, 2182 women underwent first-trimester DS screening (n=2086) or second-trimester DS screening (n=96). 117 women were screen positive, with a DS risk ratio of <1:250. The screen-positive rate was 5.36% overall and 5.23% for first trimester and 8.33% for second trimester. Of the 117 women, 26 had NIPT in private settings before or after being screened positive, 89 opted for NIPT (n=65) or invasive testing (n=24) in our hospital, and two did not have further testing owing to spontaneous miscarriage (n=1) or termination of pregnancy (n=1). Of 91 women with NIPT, 84 (92.3%) were at low risk for common aneuploidies, four were at high risk for T21 (n=2) or T18 (n=2), and three had abnormalities other than common aneuploidies. Six of the high-risk women underwent invasive testing and abnormalities were confirmed. Of the 24 women who opted for invasive testing, 14 had normal results and 10 had abnormal results. In logistic regression analysis, predictors for opting for invasive testing (rather than NIPT) were presence of abnormalities on ultrasonography (odds ratio (OR)=13.9, p=0.01), a nuchal translucency thickness of ≥3 mm (OR=7.62, p=0.01), and education level below tertiary level (OR=7.14, p=0.02).
Conclusion: In the first 12 months of implementation in United Christian Hospital, the uptake rate of NIPT as a second-tier test after positive DS screening was 77.8%, which is higher than that reported in previous studies when NIPT was a self-financed test.
Hong Kong J Gynaecol Obstet Midwifery 2022; 22(1):9-15
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