There are genetic tests and services that are available; however, they by no means will look for all genetic abnormalities. Birth defects can be from inherited factors and can also occur randomly in people with no family history of a disorder. Women over the age of 35 have the greatest risk of having a baby with birth defects. We offer genetic testing to all our obstetrical patients.
These tests are not mandatory and in some cases insurance policies do not cover them. If you would like to check coverage for genetic testing, please speak to your physician about which tests are planned and information can be given to help you find out more information.
Regardless, we cannot guarantee that your insurance company will ultimately cover these tests – coverage is variable. These tests will not tell you for certain if there are abnormalities, but will inform you as to the likelihood of an abnormality. When deciding whether you want to do the testing, we encourage patients to think about what they will do with the information they receive considering the false positive rate. On the other hand, it can be helpful information to look into further with a high risk specialist; especially if there is something that could be planned for, i.e. heart defect in Down syndrome.
Some of the disorders these tests screen for are:
- Down Syndrome – This is where there is an extra chromosome 21. This is the most frequent chromosomal disorder; commonly resulting in some degree of intellectual disability, heart abnormalities and other birth defects.
- Trisomy 18/13 – This is where there is an extra chromosome on either 18 or 13. Both result in severe developmental disability and physical disfigurement. Many of these pregnancies do not survive, and if they do, many of these newborns die in their first year of life.
- Open Neural Tube Defect – This is a major birth defect where the bones of the spine do not close around the spinal cord. This can cause varying levels of paralysis and other problems of the central nervous system.
- Cystic Fibrosis – This disorder requires both the mom and dad pass on a defective gene. If you are a carrier (meaning one defective gene and one normal gene) it is of no medical consequence to you/your child. This disorder causes severe problems with digestion and breathing. It does NOT affect appearance or intelligence.
The purpose of any of this testing would be to evaluate your risk to prepare yourself to care for a child with special health care needs or allow time to terminate the pregnancy if desired.
Non-invasive screening methods:
First trimester Assessment:
This test is for Down Syndrome and Trisomy 18. It can be done in one visit and has two parts: blood work and ultrasound. It is done between 10 weeks 3 days and 13 weeks 6 days. The first part is blood testing and the second part is an ultrasound of how much fluid is behind the baby’s neck (called a Nuchal Translucency). This must be done through a qualified center; we recommend St. Luke’s perinatology service. The results are available in about one week and the test can detect 83% of babies with Down syndrome and 80% of babies with Trisomy 18. Alternatively, a positive result does NOT mean that your baby has one of these conditions but rather that more testing may be indicated. Additional lab work is drawn between 15 and 20 weeks to evaluate for Open Neural Tube Defects. The advantage of this particular test is that it gives the earliest detection possible and therefore allows you to have the option of Chorionic Villus Sampling (CVS)
Maternal serum marker screening test
This screen is called the “quad screen”. This is a maternal blood test looking for hormone levels which lead to suspicion for Down syndrome, Trisomy 13/18 and open neural tube defects. This lab is drawn between 15 and 20 weeks of pregnancy. There is a 5% false positive rate, meaning 1 in 20 people will have a lab abnormality indicative of a problem when in fact the fetus does not have an abnormality. If there is an abnormality, you have the option of proceeding with an amniocentesis as described below.
Cell free-fetal DNA testing
The previous listed tests have generally been replaced by cell free fetal DNA testing. This is a blood draw that occurs generally at 10 weeks and beyond, there is no upper limit of gestational age to have this drawn. This test looks at fragments of the pregnancy DNA that is circulating in the maternal blood. This tests screens for Down Syndrome, Trisomy 13, Trisomy 18 and fetal sex chromosome disorders. Under certain circumstances more in depth testing can be performed with this technology. In screening for Down Syndrome this test has a 99% sensitivity, 99.95% specificity. This is still a screening test and your physician would speak to you about diagnostic testing in the case of a positive result.
This is a test of the maternal chromosomes for a panel of autosomal recessive disorders. These are disorders such as cystic fibrosis, spinal muscular atrophy and many more. Depending on personal and family history there are a different number of genes that can be tested. If a positive result is received, usually the next step would be to have your partner tested as well. Generally, to have an affected child, you and your partner would need to be carriers of the same disorder. Some women opt to get this testing done during pre-conception counseling. Once you have had this test, repeat testing is not needed in subsequent pregnancies.
Nuchal Translucency screening
This screen is done between 11 and 14 weeks. An ultrasound performed through a high risk pregnancy specialist/perinatologist is used to look at the thickness of the back of the fetus neck. This evaluation alone will find 87% of Down syndrome cases. If you combine this with blood testing in the second trimester (maternal serum screening test), 95% of fetuses with Down syndrome were identified.
This ultrasound is performed at 18 weeks of pregnancy (at the earliest) and looks at the anatomy of the baby. As long as the baby cooperates with regard to position, we can determine the gender of the baby at that time. This ultrasound can also evaluate the spine with regard to neural tube defects like spina bifida. Most major problems with the way your baby might be formed can be seen at this time; although some problems such as cleft lip/palate, clubbed feet or heart defects can be missed.
Chorionic Villus Sampling:
This is a diagnostic test performed by a specialist between 10 and 12 weeks of pregnancy. A needle is inserted through your abdomen or through a catheter in your cervix in order to reach the placenta where sample of cells is taken. These cells are then evaluated for actual chromosomes. This test cannot evaluate for open neural tube defects and 1 in 200 women will have a miscarriage as a result of this test.
This test is performed by high risk obstetric specialists and involves inserting a thin needle through your abdomen to withdraw a small amount of amniotic fluid from around the baby. This test is performed at or after 16 weeks. The cells from the fluid are evaluated for actual chromosomes of the fetus. Later in pregnancy, we can also use amniocentesis to evaluate for fetal lung maturity in cases where an earlier delivery is medically indicated. About 1 in 300 to 1 in 500 women will have a miscarriage or complication as a result of this test.
If you have any further questions or would like more information on any of the above topics, please speak with your doctor.
Coverage of genetic testing is highly variable and dependent on your insurance plan. We cannot guarantee insurance coverage for any testing or procedure regardless of what your insurance tells you.