The Facts on Prenatal Testing

Maternal Genetic carrier testing

The physicians at John A Haugen Associates are offering carrier screening for genetic diseases in women (and their partners) who are thinking about starting a family or are already pregnant. This test can screen for many genetically inherited conditions. Individuals may not have a family history of a genetic disease but they can still be a carrier of a genetic condition that can be passed on to their children. Whether or not they have an affected child depends on the genetics of the father of the child as well.

Some of the tests included are cystic fibrosis, tay-sachs disease, sickle cell disease, and spinal muscular atrophy (SMA). Certain ethnicities have a higher likelihood of being a carrier of some of these conditions. This test can also be useful to couples undergoing in vitro fertilization (IVF) to see who might benefit from preimplantation genetic diagnosis (PGD). The physicians at John A Haugen Associates can discuss this with you in greater detail. For those individuals interested in testing, we are currently recommending the ACOG (American College of Obstetrics and Gynecology)/ACMG (American College of Medical Genetics) panel. “Tandom testing” of the partner/spouse can also be coordinated to provide you with the most detailed information possible.

Prenatal Testing Summary all prenatal testing is OPTIONAL

All couples have a 3-4% chance of having a baby with a birth defect. Your risk may be less or more than this depending on many factors including age, medical conditions, medication use, and family history. These tests are looking for problems with your baby. Prenatal testing for certain disorders is optional for all couples. There are screening tests and diagnostic tests to give you more information about your specific risk in this pregnancy. Each test has benefits and risks and the options can be confusing. Prenatal testing is an area of medicine that is changing rapidly and there are new variations of tests coming out frequently. There is no test available that can identify every possible birth defect or medical condition of a baby. There is no guarantee despite any testing, that any condition can be diagnosed or that you will have a healthy baby. To follow is a brief summary of conditions that can be tested for and the types of testing available.

Types of conditions tested for:

Neural Tube Defects: this category of birth defects comprises problems with how the brain and/or spinal cord of the fetus formed. These structures develop from the neural tube of the embryo. If this tube does not close appropriately (usually occurs 30 days after conception), this type of defect can occur. These problems range from spina bifida (an opening in the spine and spinal cord causing a range of disabilities) to anencephaly (an absence of the brain). The risk of having this condition is 1/500 and does not change with maternal age.

Chromosomal abnormalities: Chromosomes are structures in every cell that carry genetic information. Normally a person has 23 pairs of chromosomes or 46 total. If a pregnancy gets too many or not enough chromosomes, problems arise. Usually these pregnancies miscarry. If miscarriage does not occur, a baby may be born with mental and physical disabilities, sometimes incompatible with life. One of the most common chromosome abnormalities is Downs Syndrome, or Trisomy 21, which is an extra chromosome 21. In this condition, there are 3 chromosome 21s instead of 2. Another chromosome abnormality that can be sometimes detected with prenatal testing is Trisomy 18, a lethal complication resulting in fetal or neonatal death. The risk of having a baby with a chromosomal abnormality increases with maternal age. However, because younger women have more babies, 80% of all chromosomal abnormalities are found in mothers less than 35 years of age. Please see the attached table at the end of this information with your age related risk.

Optional Screening Tests:

These tests DO NOT diagnose or prove there is a problem. They simply can change your risk of having a baby with certain disorders but do not give you a Yes/No that your baby does or does not have the condition tested for. There are false positive and false negative results with these tests. So, even normal tests do not guarantee the birth of a healthy baby. If you have abnormal results of these tests, one of the diagnostic tests would be offered to give you further information.

Test When Done Type of Test Benefits Risks
First trimester screening* 11-13 weeks. Results in 7-10 days. Ultrasound and maternal blood test Assess risk for Down Syndrome and Trisomy 18. Detects about 85-90% of babies with Down Syndrome. 5% false positive rate overall. More false positives with increasing maternal age. If abnormal ultrasound measurement but normal overall results, increased risk for fetal heart defects (40% risk).
Quad screen 15-20 weeks. Results in 7-10 days Maternal blood test Assess risk for Down Syndrome, Trisomy 18, and neural tube defects. Detects 80-85% of babies with Down Syndrome and 90% with Trisomy 18. 5% false positive rate overall. More false positives with increasing maternal age.
Anatomy ultrasound (recommended for all patients) 19-21 weeks. Ultrasound Assess fetus for birth defects. Detects 50% of babies with Down Syndrome. 10-15% false positive rate. Finding “soft signs” which can be associated with a chromosome problem but usually are not. A normal ultrasound does NOT rule out all birth defects.

* First trimester screening measures the nuchal translucency (fluid area behind the neck) of the fetus and 2 proteins in maternal blood. All this information is also combined with maternal age to get a risk assessment for Trisomy 21 and Trisomy 18. If you do this test, then instead of the Quad screen at 15-20 weeks we offer an AFP (alpha fetal protein) maternal blood test to screen for neural tube defects.

Optional Diagnostic Tests:

These tests are more accurate at finding a fetal problem but they are looking for specific problems. Even a normal result of one of these tests does not guarantee a healthy baby. The trade off with improved accuracy of these tests is having a risk to the fetus. Some women do these diagnostic tests after abnormal screening test results and some women do diagnostic testing without previous screening tests. These tests are performed by a high risk obstetric specialist and we will refer you if you desire one of these tests.

Test When Done Type of Test Benefits Risks
Chorionic Villus Samping (CVS) 11-13 weeks. Results in 7-14 days. Ultrasound and biopsy of placenta 99.9% accurate at diagnosing fetal chromosome disorders. Can diagnose single gene disorders if known family risk. 1/100-200 miscarriage rate. Can find placental chromosome problems which are not found in the fetus (3% risk).
Amniocentesis 15-20+ weeks. Results in 7-14 days. Ultrasound with sample of amniotic fluid around fetus via needle 99.4% accurate at diagnosing fetal chromosome problems. Increases detection of neural tube defects. Can diagnose single gene disorders if known family risk. 1/400 miscarriage rate

Optional non-invasive prenatal test (NIPT) for 3 chromosome abnormalities:

There is a new category of testing that offers a non-invasive (not amniocentesis nor CVS) testing option to look for Trisomy 21, 13, 18, and an abnormal number of sex chromosomes. A “trisomy” means that the baby has one extra chromosome, i.e. a baby with Trisomy 21 has 3 chromosome 21s instead of the usual 2. This test checks for fetal DNA in mom’s blood so it has no risk to the fetus. This testing detects more fetuses with these trisomies than the first trimester screen or quad screen while having fewer false positives (a false positive is when the test comes back abnormal even though the baby doesn’t have that problem).

Insurance coverage for this test varies. You MUST check your insurance coverage prior to having this test done.

Test When Done Type of Test Benefits Risks
Non-invasive prenatal screening (NIPS). 11+ weeks. Results in 7 days. Maternal blood test. 99.9% of cases of Trisomy 21 detected. 97% of Trisomy 18 cases detected. 79% of Trisomy 13 cases detected. Some sex chromosome abnormalities detected. Very rare false positive result. Confirmatory diagnostic testing (amniocentesis or CVS) may be recommended if abnormal result. Up to 4% chance no result is able to be given for one/all trisomies tested.

Summary

There are risks and benefits to these tests and it is an individual decision for each family whether to do any of these tests and which ones. You do not need to do any screening or diagnostic testing. The benefits of any prenatal testing include reassurance, or in the event of a problem, preparation, optimal medical management, or termination of the pregnancy. The risks including additional worrying if you have abnormal screening tests but don’t do diagnostic testing and the miscarriage risks associated with diagnostic testing. This risk of not doing any testing is not knowing about a birth defect, or a higher risk of one, before delivery.

Any ultrasound requires a specific ultrasound appointment with one of our ultrasonographers. No ultrasound is done as part of any routine prenatal visit. Please ensure that you have your appointments scheduled appropriately. Our front desk staff would be happy to confirm your appointments.

**Please check on your insurance coverage before deciding to do any test. In addition, some insurance only pays for a certain number of ultrasounds so if you decide to do first trimester screening, you may find that later ultrasounds are not paid for. It is YOUR responsibility to know your insurance coverage and pay any costs over and above that coverage.