Advocating a specific risk calculation of trisomy 18 in case of low maternal serum markers during screening for fetal Down syndrome.

Background: In France, legislation concerning pregnancy monitoring only considers screening for Down syndrome (T21), while the contingent introduction of the circulating cell free DNA test (DPNI) also allows screening for trisomies 13 and 18 with similar performances.

Methods: We retrospectively studied more than 800,000 patients among whom 7971 presented serum markers suggestive of T18 (but without increased risk of T21), of which 438 benefited from NIPT and of a complete pregnancy follow-up.

Results: We show that the use of a specific risk calculation for T18 would have improve the relevance of the prescription.

Conclusions: The generalization of this calculation would allow an optimization of the management of patients presenting a suggestive biochemical profile without significantly increasing the number of NIPT prescribed.