[tri-med] Re: AFP--always or not show the trisomy????

----- Original Message ----- 
From: "David & Tracey Pass"
>>The only definitive prenatal tests are amniocentesis and CVS
> because they test fetal cells.

Being pedantic - the CVS isnt actually testing fetal cells it tests cells 
from the placenta and therefore has a higher error rate than an amnio. That 
error is usually in the realms of detecting a mosaicism that isnt really 
there.

The placenta can (and sometimes does) have a trisomy (or mosaic trisomy) 
that the baby doesnt have. In fact part of the placenta can have a trisomy 
and part not.

The benefit of a CVS however is that it can be done earlier than an amnio. A 
CVS can be done from 11 weeks but there isnt enough amniotic fluid that 
early to do an amnio. With an amnio you have to wait until at least 16 or 18 
weeks. The downside of a CVS is that has a higher misacrriage risk than an 
amnio (about 1% higher, some say 2 or 3% higher).

The only true genetic testing of the baby prenatally is amnio (which tests 
amniocytes which contain sloughed off skin cells from the baby as well as 
some cells from the urine and gut) and cordocentesis (which is where they 
take blood directly from the umbilical cord).

Cordocentesis is by the most accurate, carries the highest risk for problems 
(it can cause the cord to bleed or cause infection) and still has an error 
rate especially if they accidentally take the mothers blood not the babys.

Nothing in life is guaranteed I'm afraid.

"We come to love not by finding a perfect person, but by learning to see an 
imperfect person perfectly"
Sam Keen

Keep Looking For Rainbows!!
   _--_|\
 /Karen \
 \ _.--._ /
          v Karen, Mum to Alex (10 years, T-18 Mosaic)
http://members.optushome.com.au/karens

                  Building ___ooOOoo__ Rainbows
                       www.trisomyonline.org
                  Families Helping Families On-line

Other related posts: