If the false positive rate were kept constant at 5% and detection rates of the tests were greater than 65%, then, given that the gestational age was estimated by the date of last period and there was a 75% uptake of amniocentesis by screen positive women,the cost per case diagnosed of Down's syndrome would be: 34,000 for the double test, 36,000 for the triple and 35,000 for the quadruple. If the gestational age was estimated by scan all the tests would cost 32,000 per case diagnosed of Down's syndrome.