How innumeracy can hurt patients

I just got this email from a patient.

Respected sir,you don't know me but I have always been a reader of your website.It has helped me to conceive in age of 34yrs. I have a daughter of 6and half yrs.As now I am pregnant with 18 weeks and living in China I GOT MY TRIPLE TEST DONE. In that report DOWNS is 1:380 and normal is1:253.AS DOWNS IS HIGH ,the doctor told me to get AMINOCENTESIS done.I got that done yesterday.THE report will take 3-4 weeks for result. Till then I am very much tensed.Can u suggest ME something.It will be great help for me.

NB Downs refers to Down's syndrome ( Trisomy 21, the commonest chromosomal error in humans). The triple test is a simple blood test used to screen pregnant women for possible fetal anomalies.

This was my reply.

I don’t think you should worry at all if the ultrasound scan is normal. The triple test is just a screening test. There was NO need for the amniocentesis at all ! A risk of 1:380 is very low – and is better than normal ! It means there is a better than 99.7 % chance ( 379:380) your baby will be normal !

The tragedy is that this patient was pushed into doing an unnecessary , risky invasive medical procedure by her doctor. The normal result of the triple test should have been used to reassure her - and instead is was misused to make her agree to an amniocentesis - a procedure which has a 1:200 risk of causing a miscarriage of a normal fetus !

The bigger tragedy is that this patient was not well-informed enough to be able to protect herself from this doctor and make the right decision for herself !