Positive Predictive Value of Screening Tests in the First and Second Trimester of Pregnancy in the Diagnosis of Trisomy 21, 18, and 13 Using Amniocentesis

Abstract

Background: The aim of this study is to analyze the positive predictive value (PPV) of trisomies 21, 18 and 13 at first and second trimester using amniocentesis for clinical practice.
 Methods:This is a descriptive cross-sectional study in which data were extracted from a cohort project of mother and infant conducted between March 2016 and February 2021 among 3110 pregnant women in Yazd city.
 Results: Out of 3110 pregnant women, 84 mothers were at high risk in the screening tests of the first and second trimesters of pregnancy and therefore were candidates for amniocentesis. None of them were detected by the positive amniocentesis method. The mean age of mothers was 33.2 years. The causes of amniocentesis included old age (45.9%), positive results of Down syndrome screening (23%), high NT ultrasound (4.9%), and pathological results of anomaly scan sonography (3.8%).
 Conclusion: In this study, the PPV was zero and the number of false positives in screening tests was 84 (100%). This may be because our population was normal and had no history of genetic abnormalities or other special conditions.