Fig. 1

Model for estimating livebirth prevalence of T21. Correction rates of natural foetal loss for women screened by amniocentesis was 25% (therefore survival to term 1−0.25 = 0.75) and foetal loss rates for women screened by CVS were approximately 32% (therefore survival to term 1−0.32 = 0.68)* each year by age of mother at the time of birth, from 15 years till 60 years old. AC_ToP termination of pregnancy following positive amniocentesis, CVS_ToP termination of pregnancy following positive chorionic villus sampling