[aaron-santos]

More false positives from ultrasounds could lead to more amniocentesis true positives simply by increasing the number of amniocentesis performed. Without more information it's not possible to tell.

[kovac]

But since more babies should be born without DS, despite more diagnoses of DS due to more tests, shouldn't the negatives also increase (more) after the amniocentesis? I expect both positives and negatives to increase with the increase in negatives being more than the increase in positives.

[lifeisstillgood]

Thank you that's my point better put. Unless they uncover a hidden pool of Downs cases (unlikely) this was an increase in false positives leading to an increase in amniocentesis leading to an increase (1/300) of preventable foetal deaths. I think.

[aaron-santos]

I was careful to say true positives rather than true positive rate. This is why without more information it is hard to know exactly what is going on.

[mkl]

If you get a true positive from amniocentesis, the positive ultrasound would have been a true positive too, though, right?