The study group was a convenience sample where all of the pregnant women invited to participate had either declined Down syndrome screening or had already undergone screening and had screened low-risk.
Úrtakið var hentugleikaúrtak og þeim konum var boðin þátttaka sem höfðu annaðhvort hafnað fósturskimun eða fengið niðurstöðu um litlar líkur á litningagöllum.