Evolution of Down Syndrome Prenatal Screening Clinical Practices in Québec

Prenatal screening for Down syndrome (DS) has evolved greatly over the last decades with the improvement of first- and second-trimester serum screening and the introduction of cell-free fetal DNA. This study aimed to estimate the impact of such changes on practices.

This retrospective cohort study included fetuses and newborns diagnosed with DS between 2005-2007 and 2015-2017 in the single obstetrical care centre in Québec City. Data were collected on the prenatal screening method, diagnosis, and delivery. The median was compared between the study periods.

Complete clinical data were available for only 78 (66%) of 119 cases of DS. Significant changes were observed in screening methods, including an increase in the use of first-trimester serum, ultrasound, and cell-free fetal DNA. No significant changes were noted in terms of gestational age at diagnosis (median [interquartile range; IQR]: 17.0 [16.0-20.9] weeks in 2005-2007 vs. 17.9 [16.3-22.5] weeks in 2015-2017; P = 0.49) and delivery or termination of pregnancy (median 20.9 [IQR 18.0-23.3] weeks in 2005-2007 vs. 21.3 [18.4-23.4] weeks in 2015-2017; P = 0.46). The methods of diagnosis did not change significantly over the decade, with amniocentesis used 85% and 79% of the time, respectively (P = 0.19).

The increased use of first-trimester screening and cell-free fetal DNA tests was not associated with earlier diagnosis of DS or earlier delivery or termination of pregnancy. The use of chorionic villus sampling should be encouraged for DS diagnosis when indicated because it could reduce the gestational age at diagnosis and termination if requested.