Ask the Midwife

Question:

I am 8 weeks pregnant with my first baby and just had my new OB visit. I am confused about genetic tests that are offered. Are these required? What do you recommend? How accurate are they? What is the difference between a screening test and a diagnostic test? Will my insurance cover this type testing? 

 

Answer:

Congratulations on your pregnancy! It is our goal that you feel informed about all of your options during your pregnancy and have the confidence to make the right choices for yourself and your baby. Unlike the basic blood tests that we ask you to get during pregnancy so we can take the best care of you, the genetic tests are not required. We can give you information and guidance but we do not make specific recommendations, as whether or not to have genetic testing is a very personal choice. 

 

Genetic tests come in two different categories: screening tests and diagnostic tests.

Screening tests can tell you if there is a chance that your baby is affected by specific disorders but not whether it is certain. If a test comes back indicating that there is a higher chance of a problem, further testing must be done to verify whether or not there is actually a problem. Screening tests have different rates of false positive results, depending on the test. Diagnostic tests tell you for sure whether your baby is affected. Diagnostic tests are not generally the first line test done, as they are invasive (small chance of miscarriage) and expensive. Screening tests do not have the potential to cause harm to the pregnancy. 

 

Since you are still early in your pregnancy, you have many options to choose from. One option is the NIPS Cell Free DNA test. This is a blood test, so you would have your blood drawn for this. It can be done after 10 weeks and tests for Down syndrome, Trisomy 18, Trisomy 13, sex chromosome abnormalities, and can determine fetal sex. This is a screening test, and has a detection rate of 98-99%. If there is a positive result, further testing (ultrasound or invasive testing) would be required to be sure of the diagnosis. This test is not likely to be covered by insurance. Those on Medicaid can apply for a reduced rate of $149 for the test; others will pay $249 unless they are determined to be high risk in which case higher costs could be incurred. 

 

Another option for genetic screening is Maternal Serum Screening. This can be done in two ways. The first option is to have a special ultrasound at 11-13 weeks to check for thickening on the back of the baby’s neck, and then follow up with a blood test. This screens for Down syndrome, Trisomy 18 and spinal cord defects. This special ultrasound requires a trip to the maternal fetal medicine specialists. The detection rate is 80-90% and most insurances will cover this, but you of course have to check with your particular insurance. The second way of doing a Maternal Serum Screen is through a blood test at 15-21 weeks of pregnancy. This test is called MSAFP-4 and can be ordered by your midwife or OB physician. This test screens for the same disorders but has a slightly lower detection rate. There is a false positive rate of 6.6% with this test (indicating there could be a problem when there is not). As with other screening tests, if there is a positive result, high tech ultrasound and/or invasive screening would be needed. Most insurances will cover MSAFP-4. 

 

Carrier screening will also be offered to you. This type test does not test the baby. It tests the mother to see whether or not she carries certain diseases. This can include Cystic Fibrosis, Spinal Muscular Atrophy, Fragile X Syndrome, Sickle Cell Anemia and Thalassemia. Often these tests are indicated based on ethnicity. People of certain ethnic backgrounds have a higher incidence of some inherited disorders. If a woman is determined to be a carrier, the father of the baby would need to be tested as well to determine the risk to the baby. There could be a referral to a specialist for counseling in this case. Insurance may or may not cover this type testing; check with your insurance company. 

 

Finally, diagnostic testing is usually done as a follow up to screening tests, to verify whether there is actually a problem, but may be offered to certain women as first line testing based on risk factors.

 

This type testing is invasive and there is a small risk of miscarriage. Amniocentesis is a test that is done from 15 weeks on and involves removing some amniotic fluid from the uterus and testing the fetal chromosomes. There is a risk of 0.3-0.5% of miscarriage from this procedure.

 

Chorionic Villus Sampling (CVS) is done between 11 and 14 weeks and involves taking a sample of placenta and then looking at the chromosomes for possible abnormalities. The risk of miscarriage is slightly higher with CVS, at 0.5 to 1%. This test can tell you definitively if there is a problem.

 

However, keep in mind that genetic screening and diagnostic tests do not test for all disorders. Heart defects, limb abnormalities, cleft palate and autism are all examples of conditions that cannot be diagnosed by genetic testing. Ultrasound can often but not always diagnose fetal malformations. Insurance may or may not cover this type of testing. 

 

The question of whether to have genetic screening and/or diagnostic testing done is a very personal one. It is important to think about your options and what you feel comfortable with, as well as considering what you would do with the information you receive from the testing. There are women who want to have every test available. Some women feel that they want the testing so they can be prepared if there is a problem. Some women would choose not to carry a baby with a severe disorder. There is also the chance that getting a false positive result could cause anxiety throughout the pregnancy and make the pregnancy less enjoyable. Some women decline testing altogether. If you have risk factors for specific disorders you may be encouraged to have testing but ultimately the decision is yours.

🡆 Elizabeth Withnall, CNM has been practicing midwifery for 29 years, first as a licensed midwife attending home and birth center births, then later as a certified nurse midwife, in the hospital setting.