The Facts on Prenatal Testing

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The Facts on Prenatal Testing

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. 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. 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 done that a condition is diagnosed or that you will have a healthy baby. The following information is a brief summary of conditions that can be tested for and the two categories 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 three chromosome 21s instead of two. 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.

Optional Screening Tests:

These tests DO NOT diagnose or prove there is a problem. They simply can change your estimated 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	Benefits	Risks
First trimester screening*	10- 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)	18-22 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 Diagnotic 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 usually performed by a high risk obstetric specialist and we will refer you if you desire one of these tests.

Test	When Done	Type	Benefits	Risks
Chorionic Villus Samping (CVS)	10-12 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	1/300 miscarriage rate

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.