(quiet, upbeat music)
- I'm Carrie Couyoumjian.
I'm one of the genetic counselors
in the fetal diagnostic center.
There are many different types of prenatal tests
that are available.
And the lists of these tests can become overwhelming.
None of these tests are required
and it's important to remember that as a patient.
It's our job as genetic counselors
to help patients decide if any of these tests
are things that they would like to pursue.
So the two categories of testing are
screening tests and diagnostic tests.
Screening tests are not invasive
and they pose no risk of pregnancy loss.
And on the other hand,
they don't provide diagnostic information.
They give you an idea of a risk for certain conditions.
Diagnostic tests do come with
an associated risk of miscarriage.
However, they also do provide diagnostic information.
In terms of screening options, the first option available,
with respect to gestational age,
would be a first trimester screen.
This is performed between 11 and 14 weeks gestation
and it involves an ultrasound and a blood test.
It provides risk assessment information for Down Syndrome,
which is a chromosome problem,
and two other chromosome problems,
which are less well known to most people
called trisomy 13 and trisomy 18.
There are some tests that can be used
to combine the first trimester assessment
with a second trimester blood draw.
Those are called integrated screen or sequential screens.
And then there are other tests
which can be done in the second trimester only.
These days, we're most often offering quad screening,
which is just a second trimester blood test.
And it provides risk information about Down Syndrome,
trisomy 18, and neural tube defects,
the most well known of which is spina bifida.
The results of all of these
different types of screening tests
are reported out in the form of a ratio or percentage.
So they don't give a yes or a no answer,
but they provide a patient with
an idea of their baby's risk for certain conditions.
Each test has its own associated detection rate
and false positive rate.
And patients can use the results of these screening tests
to help them decide whether or not they'd like to
go on with any further diagnostic testing.
So diagnostic tests actually provide a diagnosis,
as opposed to a risk assessment.
These tests can be used to identify
chromosome abnormalities, genetic mutations,
biochemical abnormalities, among other things.
Diagnostic tests are considered invasive,
so there is an associated risk of miscarriage.
In terms of gestational age,
the first diagnostic test we can offer is called CVS,
or chorionic villus sampling.
This is actually a placental biopsy.
And we can do this as early as 10 weeks
and into the 13th week of gestation.
The physician can go in either cervically or abdominally
to obtain some placental tissue.
And this is what we'll use for testing.
The associated risk of miscarriage is about 1%,
which combines the actual risk of the procedure
with the baseline risk of miscarriage
at that time in pregnancy.
The second diagnostic test that we can offer
is something called an amniocentesis.
And this is probably a little bit
better known to most people.
It can be done starting at 15 weeks gestation
and any time beyond.
It involves a sampling of amniotic fluid to do testing.
Within the fluid are fetal cells
and that's actually what material is used
to perform the genetic tests.
Amniocentesis is always done abdominally with a needle
and it's associated with about
a one in 400 risk of miscarriage.
Both CVS and amniocentesis are done
under ultrasound guidance
so the physician has a window into the procedure.
Results of either test are available typically
between about 10 and 14 days after the test is done.
Some testing can take longer if it's not routine or typical.
And we usually report those results up
directly to our patients.
Another type of diagnostic testing is called PUBS,
or percutaneous umbilical blood sampling.
It's done a little bit less commonly
because it does have a higher miscarriage rate.
And it's really not a test that's necessary
to get chromosome information.
It's more often used for other, more rare indications.
We as genetic counselors work with you and your physicians
to help you make decisions about whether these tests are
things that you might wanna consider.