Participants
This study is a subgroup analysis of a multi-center prospective cohort designed to investigate the cost-effectiveness of various prenatal test strategies after the introduction of cfDNA screening. The protocol was published prior to the analysis of this study [8]. In brief, the prospective cohort study was performed in 12 different secondary and tertiary health care institutions between June 2016 and October 2018. Singleton pregnant women who underwent NT ultrasound examinations were included and counseled regarding fetal aneuploidy screening or diagnostic test before 24 gestational weeks. The cases with unknown pregnancy outcomes were excluded in our study.