prenatal screening and diagnostic

Prenatal Screening and Diagnostic Tests

Prenatal Screening and Diagnostic Tests

by Jessica

[While pregnancy screening may not seem tied to infertility, we felt

that women who have experienced infertility or a prior pregnancy loss

uniquely approach these tests with difficult decisions to make. Not

everyone chooses to take these screening or diagnostic tests. And not

everyone who takes these tests receives the results they want to hear.

Some women who have worked hard to become pregnant may not want to

take any unnecessary risks and choose not to test. Other women may

know that they are at risk for a chromosomal disorder and may want to

know whether or not the fetus has that chromosomal disorder.

Regardless, diagnostic testing can be a very emotional experience.

Make sure you have a good support system in place as you decide

whether or not to embark on testing that will remain with you no

matter what decision you make based on the information gained from

these tests.]

Test or Not to Test?

Once pregnant, you are faced with an entirely new set of decisions.

One of those is whether to do prenatal screening and/or diagnostic

tests such as the Ultrascreen, AFP screen, CVS (Chorionic Villus

Sampling) or Amniocentesis.

These tests normally tell you that your baby is just fine - that you

don't have to worry about Down Syndrome (Trisomy 21) , Trisomy 18

(Edwards Syndrome), neural tube defects , or other serious conditions

that these tests can screen for or diagnose. On the other hand, these

tests may tell you that your baby does have one of these conditions,

giving you the opportunity to decide whether to terminate the

pregnancy or, if the condition is compatible with life, the

opportunity to prepare for a special needs baby.

Maybe it took a long time to get pregnant, or you've experienced

pregnancy losses in the past. These experiences could influence your

decisions on prenatal testing.

Screening tests (Ultrascreen or nuchal translucency test and AFP)

don't pose any kind of risk, but they only give you odds of whether or

not there is a problem. They can't give you a yes or no answer. And

many women lament so-called "false positives" - when the tests tell

you that your baby's odds of having a particular condition are higher

than they would normally be for a woman of your age. Hearing that your

baby may be sick, but not knowing for sure can be scary.

In fact, the idea of hearing news like this which is not definitive is

why some women skip the screening tests and go straight to the

diagnostic tests. Diagnostic tests (CVS and amniocentesis) are

invasive and do pose a risk of complications and even pregnancy loss.

The odds of complications are usually said to be 1 in 200 or 1 in 300.

But while these tests do carry a risk, they have an advantage over the

screening tests -- they provide a definitive yes or no answer. If the

amnio says the baby is OK, that means you can be absolutely sure the

baby is free of certain conditions. Both screening and diagnostic

prenatal tests, performed in the first and second trimester, look for

abnormalities of the fetus. Some of these abnormalities include neural

tube defects, the most well-known of which is Spina Bifida; others are

chromosomal problems such as Trisomies (Trisomy 21, Down Syndrome and

Trisomy 18, Edwards Syndrome are the most common of these); or some

other defect. Some defects will inhibit the baby's quality of life and

some of these conditions are incompatible with life.

What to Expect

Ultrascreen and AFP are screening tests. The Ultrascreen relies on a

blood draw and ultrasound. The AFP also relies on a blood draw, which

is sometimes supplemented with a Level II ultrasound. The Ultrascreen

is performed at the end of the first trimester. The ultrasound

measures the nuchal translucency, the fluid under the skin at the back

of the fetus's neck. The blood test measures the levels of two

substances in the mother's blood - free Beta-HCG and PAPP-A. By

looking at these values together, doctors can determine the risk of

certain disorders. According to Genecare, the Ultrascreen detects 91

percent of Down Syndrome and 97 percent of Trisomy 18. In addition,

Genecare says Ultrascreen reduces so-called "false positives" to 2.5

percent.

The AFP (Maternal Serum Alpha Fetoprotein test, also known as the quad

screen because it measures four substances in the mother's blood) is

performed during the second trimester, between 15 and 20 weeks. It is

less accurate than the Ultrascreen (with the exception of neural tube

defects). The AFP test is 80 percent accurate for neural tube defects,

60 percent to 80 percent accurate for Down Syndrome and 60 percent to

80 percent accurate for Trisomy 18. When women complain about "false

positives" it is usually from the results of the AFP.

These screening tests pose no risk to the developing fetus, but they

are also not definitive. They give the patient "odds" of whether their

baby is healthy or not. For example, the screening tests will tell you

that there may be a 1 in 400 risk of having a baby with Down. But they

can't tell you for sure. Still, because there is no risk, they are a

popular first step for many patients.

Diagnoistic tests include CVS and amniocentesis. The diagnostic tests

are invasive and can pose a risk of complications. These diagnostic

tests are generally recommended for women 35 and older because that is

when the odds of having a fetus with one of these conditions cross

over with the risk of complications from the tests.

CVS is performed at the end of the first trimester and is considered a

little more invasive and more likely to cause complications than

amniocentesis, which can be performed starting at 16 weeks. However,

there are a handful of practitioners across the United States who are

considered to have similar complication rates for CVS as for amnio -

i.e. 1 in 200 or 1 in 300. If you are considering a CVS, it is worth

seeking out one of these physicians.

During a CVS, an ultrasound technician performs an abdominal

ultrasound to show the doctor the location of the fetus and placenta.

Depending upon the location of the placenta (which is what the doctor

wants to access), the doctor will insert the needle either into the

woman's abdomen or through the cervix to reach the placenta. A local

anesthetic is used to numb the area. Then the doctor inserts the

needle. Once the placenta is reached, the doctor performs a pumping

action with a device attached to the needle to "sample" a bit of the

tissue. It takes a minute or so once in place. The doctor will show

you a vial of the pinkish fluid that should be labeled with your name.

Then they will clean you up and you are done. You are on bed rest for

the rest of the day.

An amniocentesis uses similar techniques - local anesthesia,

ultrasound, a needle through the abdomen (never the cervix for this

one). With this test the doctor retrieves a sample of amniotic fluid.

Again, the doctor should show you a vial of the liquid labeled with

your name. And again, you are on bed rest for the rest of the day.

Whether to pursue any of these tests or screenings is an individual

decision. Keep in mind that odds are only odds. If odds are 1 in 400,

somebody has to be that one, whether its odds for a genetic defect or

odds of complications from one of the diagnostic procedures.

It takes a week to 10 days to receive the results back. For amnio and

CVS some practices offer a preliminary result called FISH for an

additional fee that comes back in about a day for those who are extra

anxious about the results.

Personal Tips

If you are considering a CVS instead of an amnio, it's a good idea to

schedule it as soon as you see the baby's heartbeat on the six week

ultrasound. The top-notch CVS doctors' schedules fill up quickly.

Keep in mind that you can always cancel the appointment later - for

example, if you get excellent Ultrascreen results, or even if you just

change your mind. But it will be tough to book a last minute

appointment with someone who is really good, and you want someone who

is really good.

If it is important to you to know the results in at the end of the

first trimester instead of the middle of the second trimester, the

Ultrascreen and CVS are the way to go.

For my IVF pregnancy, my RE didn't have a lot of information to give

me about prenatal testing and by the time I got in to see my OB at 10

weeks or so, it was too late to schedule a CVS. So I opted for the

amnio. I was afraid of false positives so I skipped the screening

tests. The amnio came back positive for Trisomy 18 which is a

condition incompatible with life. We ended up terminating the

pregnancy. And let me tell you, there's a big difference between

terminating at 12 weeks and terminating at 18 weeks, and I'm just

talking about emotionally.

For our FET pregnancy we did all the screening tests, the Ultrascreen

and the AFP. And we did the CVS. I did a lot of research on who to go

to for the CVS.

When searching out a doctor for CVS, call the perinatologist practices

that perform the procedure and ask to speak to a genetic counselor.

Tell the counselor about your infertility, how long and hard you

fought for this pregnancy, etc. Then ask the counselor how many CVS

procedures each doctor performs each year. The higher the number the

better. (The doctors who did my IVF pregnancy amnio did 50 CVSs per

year while the ones I eventually went to for my FET pregnancy CVS did

300 a year. With this information in hand, I chose to take the hour

drive to the more experienced doctor rather than the 20 minute drive

to the 50-per-year doc.) You can also ask the genetic counselor about

the loss rates for the practice for amnio and for CVS. (They probably

won't tell you each doctor's loss rates.) Finally, ask the counselor

who she would go to (or who he would send his wife to see.)

Whatever prenatal testing path you decide to take - Ultrascreen, AFP,

amnio or CVS - you may be scheduled for an appointment with a genetic

counselor before your screening test or your diagnostic procedure. The

counselor will ask questions about your family health history, any

drugs you've used during the pregnancy, and similar questions. The