Early detection of pregnancies at high risk for trisomy 21 (Down syndrome) is the primary target of prenatal aneuploidy screening since this syndrome is the most common autosomal trisomy among live births.
The prevalence of the syndrome in live births is about 1/600 for Down syndrome and 1/4000 for trisomy 18). Prevalence increases with increasing maternal age.
In terms of counselling we issue SASOG guidelines on prenatal screening.
The following information related to prenatal screening is discussed, as appropriate, during prescreening and postscreening visits.