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 genetic counselor will also likely tell you about your odds of various conditions and what those conditions are. And the counselor is the one who will call you with the results.