Determining strategy of the non-invasive prenatal screening for chromosomal defects

Xiromeritis PN¹, Tsapanos VS²

1Department of Obstetrics and Gynecology, Catholic University of Louvain, Louvain, Belgium

2Department of Obstetrics and Gynecology, University of Patras, Patras, Greece

Correspondence: Xiromeritis Panayotis, 27 Kambouridou St, GR-55236, Thessaloniki, Greece. E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.






The need to reduce the rate of invasive screening (chorionic villous sampling, amniocentesis), and to detect the high risk pregnancies for chromosomal anomalies as early as possible, led to the concept of the sequential non-invasive screening, based on the Bayes theorem. The numerous non-invasive screening tests for chromosomal defects, should provide the calculation of a global risk enclosing all the previous calculated risks from each screening test which took place in the past, under the condition that the findings of each test are independent the one from the other. To date, there are only four studies providing the likelihood ratios for each ultrasound finding, which are used for the calculation of the global risk for chromosomal anomalies. However, due to differences on the values of the likelihood ratios among these four studies, probably due to the lack of harmonization of the ultrasound detection criteria, there is not enough evidence for the  generalization of their use in clinical practice. 

Key words: ultrasound; prenatal screening; chromosomal defects