00:00
Hi, now we're going to discuss
screening for Down syndrome.
00:07
So it's three ways that we
screen for Down syndrome
in pregnancy.
00:10
We're going to discuss
those methods and talk about
why we would choose
one over the other.
00:14
So the first is the free fetal DNA test.
00:18
Basically, we have found
that there is free fetal DNA
circulating in mom's blood.
00:23
So mom's blood is drawn,
usually after 10 weeks of gestation
and you're able to see
the actual carrier type
of the fetus.
00:30
So you know with a 99% accuracy,
if the fetus has Down syndrome.
00:35
You're also able to find out
the sex of the baby
at that time.
00:39
So the next option for screening
is integrated, sequential,
or contingency screening.
00:44
These are all
grouped the same way.
00:46
But they are performed just
a little bit differently.
00:48
And it can be confusing.
00:49
So let's go over that.
00:52
So this test is performed
between 11 weeks and 13 weeks
and 6 days.
00:56
Has a detection rate of 96%.
00:58
Now the test involves performing
a test called
the Nuchal Translucency.
01:02
That's an ultrasound that
measures the skin fall behind
the baby's neck.
01:06
That is done along with blood
work, PAPPA and beta-hcg.
01:11
Now the difference in the test.
01:13
So the integrated screening
takes the result of
that 1st trimester test.
01:17
Again the nuchal translucency
and those two hormones PAPPA
and beta-hcg.
01:22
And looks at the blood work
at the 2nd trimester which is
essentially the quad screen,
integrates them together,
to give a patient's risk
of having a fetus
with Down syndrome.
01:32
Now this is done as probability
so there is no value that's
high or low,
correct or incorrect.
01:37
Because this is
done as probability.
01:40
Sequential screening means that
you take the results of
the 1st trimester,
you get a result.
01:45
You take the results
of the 2nd trimester
and get a result.
01:50
And overall you're
given a result.
01:53
That's a little bit different
than the integrated.
01:55
Where with integrated
you don't get a result
until the 2nd trimester.
01:59
The contingency screen is
done in the 1st trimester.
02:03
And if the risk of having
Down syndrome is low,
the 2nd trimester test
is not done.
02:08
Only an alpha-fetoprotein
is done in 2nd trimester
to determine if there is a risk
of nuchal translucency.
02:14
Together these each
have a detection rate
of about 95 to 96%.
02:19
The 3rd test is the Quad screen.
02:22
This is performed between 15
weeks and 22 weeks and 6 days
of gestation.
02:27
Mom's blood is drawn,
looking for four different hormone
levels.
02:31
That hcg, estriol, inhibin
A and alpha fetal protein.
02:35
This has a lowest
detection rate, it's 81%.
02:39
And again this is done
as probability.
02:41
So it looks at a mother of that
ethnicity, at that gestational
age with those four hormone
levels to tell the probability
of the baby having
Down syndrome.
02:51
So you can see amongst the three
tests, the free fetal DNA
is the most accurate.
02:57
However, because it is a little
bit newer,
it is the most expensive test
of the three.
03:02
We do recommend this test
for our women
that are over 35 years old as
they have an increase
risk for Down syndrome.
03:09
The Quad screen can be used if
a patient enters pregnancy after
13 weeks and 6 days and is
not able to get the integrated
sequential or contingency screen.
03:23
Now these previous discussed
tests are meant for
screening purposes only.
03:29
So if they are abnormal then
invasive testing is recommended.
03:33
So what are options
for invasive testing.
03:36
Well, there's two.
03:37
Chorionic villi sampling
and Amniocentesis.
03:40
So Chorionic villi sampling is
performed between 10 to 14 weeks
of gestational age.
03:45
And as you can see here
in the picture,
a needle is inserted into
mom's belly
and there's blood that's drawn
from the chorionic villi.
03:51
Carrier type is performed
to see if the fetus indeed
has Down syndrome.
03:56
The risk of this procedure
is pregnancy loss.
03:59
But we are able to do
an early gestation.
04:02
The next invasive test
is amniocentesis.
04:06
Now with this in a similar
manner, as you can see here in
the picture, a needle is
placed inside mom's belly.
04:13
Amniotic fluid is drawn.
04:15
And again the carrier
type is performed.
04:17
This test is usually down
around 15 weeks gestational age.
04:20
And again it is confirmation
to determine the patient
has a fetus with Down syndrome.
04:25
The risk to go along with
this procedure are bleeding,
infection, placental abruption
and again fetal loss.
04:31
It was previously thought that
with chorion villi sampling that
there was an increased risk
of fetal loss compared
to amniocentesis.
04:38
But now we know that the risk
is about the same.
04:42
So let's go through
a study here.
04:45
A 24 year old gravida 1 para 0
female at 8 weeks and 3 days
of gestation, presents
for an antenatal visit.
04:53
She has a sister
with Down syndrome.
04:55
And is concerned that the
baby may be at increased risk.
04:58
The best non-invasive screening
option for this patient is:
A. Free fetal DNA.
05:05
B. Integrated screening.
05:07
C. Quad screen.
05:09
or D. Amniocentesis.
05:11
Well, let's think about
this options.
05:13
The free fetal DNA, we've
already said,
has a 99% detection rate
for Down syndrome.
05:19
Integrated screening
has about a 95%.
05:21
And then Quad screen
has about an 81%.
05:25
Amniocentesis is the most
accurate,
because it is looking
at the carrier type
and it is the test for diagnosing
Down syndrome.
05:32
But we have to go back to
the stem of our question.
05:34
Amniocentesis is not
a non-invasive test.
05:38
So based on our options,
the answers is A.
05:41
The Free fetal DNA test.