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

----- Original Message ----- 
From: "Therese"
> I had a mom contact me and is asking several questions on why her
> "Angels" syndrome did not get picked up when she had several
> ultrasounds...and the AFP....

The AFP test was never designed to detect any of the trisomies. It was 
originally developed to detect open neural tube defects. As a side benefit 
they found that some other conditions were being picked up, but always with 
a much higher error rate than the neural tube defect.

In the AFP test a high AFP can indicate an open neural tube defect, a baby 
who is small, destined for a pre term or still birth, or simply that it is 
twins. Low can indicate T-18 OR Down Syndrome. With T-13 the AFP is usually 
normal.

A high AFP can even simply indicate that you have certain forms of cancer. 
Its far from specific.

To try and develop the test even further they started adding in other 
values, that is estriol and hCG (yep that stuff which tells you you are 
pregnant). Hence the name triple screen (they are testing three different 
substances in the mothers blood)

Low AFP and Low Estriol but high hCG is indicitive of T-21
Low AFP, Low estriol and low hCG - T-18
Normal AFP, and low hCG - T-13 (they dont have a "norm" value for estriol in 
T-13)

there are no values for Angelman's syndrome at all - they don't even pretend 
that the AFP will pick that up (Angelman's is actually a deletion)

Once they get these values they use a very fancy algorithm to calculate the 
risk. This algorithm takes into account the gestational age (and it has to 
be spot on), the mothers weight, age and all sorts of things. The end result 
is that they get a risk - usually expressed in percentages.

Its that percentage which determines what they will recommend, that is don't 
worry, have a level 2 ultrasound or an amnio. Its far from being an exact 
science and an abnormality is only an indication that they should do further 
testing.

The AFP alone is very unreliable but even with the triple screen it is 
notorious for having a high false negative or false positive. Thats in part 
why they often only do the AFP for mothers under 35 and a triple screen only 
if their is a concern with the AFP.

The problem with Angelman's is that even if they had done an amnio they 
probably wouldnt have picked it up. With an amnio they usually do a FISH 
test these days for the "common" defects - T-21, T-18, T-13 and Turners 
Syndrome (monosomy X). And these are pretty much the only things that they 
are looking for with a g-banding karyotype as well. If you are lucky they 
may pick up other gross anomalies like a translocation but I really doubt 
that they would pick up Angelman's - as I said its a deletion and a fairly 
small one.

Sorry that sounds really blunt but its hard to put the technical stuff 
sensitively.........

> Question....Does the AFP always catch the trisomy syndrome?

Absolutely not. Their are lots and lots of false positives and false 
negatives, in fact some doctors even doubt the validity of using the test at 
all. Many only do it because they fear litigation if they don't. Some 
doctors don't even understand it at all - eg in my case it was done when it 
shouldn't have been because I was 22 weeks (its only even vaguely accurate 
if done between 16 and 20 weeks) and when they got the results they didnt 
understand them so ignored them. They shouldnt have because my AFP was low 
for 20 weeks and because it was done at 22 weeks it was even more indicitive 
of T-18 (the AFP should rise as the pregnancy progresses)

> Anyone have a normal AFP and then have a trisomy child?
> She was told her child was t13

Yes, many many people have normal AFP's and still have a child with a 
trisomy - if you look at the values I quoted earlier a normal AFP with a low 
hCG is indicitive of T-13 BUT its definitely NOT a diagnosis. Chances are 
she was told that their was an increased risk of T-13 and so advised to have 
an amnio or ultrasound. But as I also said earlier the amnio probably would 
have said the baby didnt have T-13 and I doubt that it would have picked up 
the Angelman's without specific indicators which probably wouldnt have been 
seen till after birth.

"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: