Genetic Testing vs. Screening

How can I decide what’s right for me?
The American College of Obstetricians and Gynecologists now recommends that women of all ages be offered first-and second-trimester screening and diagnostic testing options. Your practitioner, our perinatologist, nurse, or genetic counselor may have discussed the pros and cons of the available approaches with you. But ultimately, whether or not to test is a personal decision.

Many women opt for screening and then make a decision about diagnostic testing based on the initial results. Other women opt for diagnostic testing right away. (They may know that they’re at high risk for a chromosomal problem or a condition that can’t be detected by screening — or they may just feel that they want to know as much as possible about their baby’s condition and are willing to live with the small risk of miscarriage to find out.) Some women decide to have no screening or testing.

If you opt for screening first, you can then decide — with the help of your practitioner, perinatologist, nurse, or genetic counselor — whether your results indicate a high enough risk that you want to have CVS or amniocentesis to determine whether a problem exists. You’ll need to weigh your need to know about your baby’s condition against the small chance that diagnostic testing could cause a miscarriage.

There’s no one right decision. Individual parents-to-be have different feelings about what risks are acceptable and may arrive at different conclusions when facing the same set of circumstances.

If I choose diagnostic testing, how do I decide between amniocentesis and CVS?
Both tests can tell you whether your baby has a chromosomal problem or certain genetic disorders.

CVS is done earlier in pregnancy (usually between 11 and 13 weeks), so you can find out sooner about your baby’s condition and chromosome makeup. If everything’s okay, your mind will be put at ease that much sooner. Or, if there is a serious problem and you opt to interrupt the pregnancy, you’ll be able to do so while you’re still in the first trimester.

On the other hand, you may prefer to wait for the results from second-trimester screening before having an invasive test. At that point, amniocentesis would be your only option.

Other considerations may influence your decision as well. For example, if you’re at high risk for having a baby with a spinal defect, a special ultrasound exam should exclude the diagnosis without the need for an amniocentesis.

CVS is generally thought to have a slightly higher miscarriage rate than amniocentesis.

Before making a decision, you, may want to discuss all of these issues with your partner, your health practitioner, and possibly a genetic counselor.

What disorders and defects does amniocentesis and CVS detect?
Amniocentesis and CVS are used to detect:

• Nearly all chromosomal disorders, including Down syndrome, trisomy 13, trisomy 18, and sex chromosome abnormalities (such as Turner syndrome and Klinefelter syndrome). Amniocentesis is more than 99 percent accurate in diagnosing these conditions.

• Several hundred genetic disorders, such as cystic fibrosis, sickle cell disease, and Tay-Sachs disease. The test is not used to look for all of them, but if your baby is at increased risk for one or more of these disorders, in most cases amniocentesis can usually tell you whether he/she has the disease.

Amniocentesis does not detect birth defects such as heart malformations or a cleft lip or palate. However, many structural defects can be picked up on the second-trimester ultrasound that’s routinely done for every woman having an amniocentesis.

What factors would put me at increased risk of having a baby with a genetic abnormality or disorder?

Some factors to consider include:

1. Down syndrome screening results – You had a screening test that indicated your baby is at a higher than average risk for Down syndrome or another chromosomal problem.

2. Ultrasound results – An early ultrasound showed that your baby has structural defects associated with a chromosomal problem.

3. Carrier screening results – You and your spouse are carriers of a recessive genetic disorder such as cystic fibrosis or sickle cell disease.

4. Your history – You’ve previously been pregnant with a child with a genetic abnormality and may have a higher risk of this happening again.

5. Your family history – You or your partner has a chromosomal abnormality or genetic disorder or a family history that puts your child at increased risk for genetic problems.

6. Your age – Anyone can have a baby with a chromosomal abnormality, but the risk rises with the mother’s age. For example, your likelihood of carrying a baby with Down syndrome ranges from about 1 in 1295 at age 20 to 1 in 82 at age 40.