SHOULD I HAVE A SCREENING TEST FOR DOWN SYNDROME DURING PREGNANCY?
- dileepn50
- Jul 20, 2020
- 8 min read
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Literature review current through: Jun 2020. | This topic last updated: Apr 23, 2019.
INTRODUCTION
This topic provides information about prenatal screening for Down syndrome to help you decide if you want to undergo this test.
More detailed information about Down syndrome screening tests is available by subscription. (See "Down syndrome: Overview of prenatal screening".)
WHAT IS DOWN SYNDROME?
The first decision you need to make is: Do you want to know, before birth, whether your developing baby has Down syndrome? It may help to review some facts about this condition. More detailed information is available separately. (See "Patient education: Down syndrome (Beyond the Basics)".)
●Down syndrome is the result of an extra number 21 chromosome. The extra genetic material causes the changes that characterize the condition.
●This condition occurs in approximately 1 in 500 births. It is more common early in pregnancy, with approximately 1 in 350 pregnancies affected in the late first trimester, but some of these fetuses die before birth.
●Most people with Down syndrome have mild (intelligence quotient [IQ] 50 to 69) to moderate (IQ 35 to 50) intellectual disability (mental retardation), meaning that the person can often do things on their own; however, most need supervision throughout their lives.
●People with Down syndrome have characteristic facial features, meaning that their facial features are often similar to those of other people with Down syndrome but are slightly different from people without Down syndrome.
●People with Down syndrome may have birth defects, such as problems with how the heart or intestines develop. Other medical problems such as epilepsy, leukemia, thyroid problems, and Alzheimer's disease can also develop.
●The average lifespan for an individual with Down syndrome is approximately 50 to 60 years.
Could my baby have Down syndrome?
●A woman of any age can have a baby with Down syndrome, but the chance gets higher as a woman gets older.
●Down syndrome usually does not run in families, but you should inform your doctor or nurse if you or your partner has a family member with Down syndrome.
WHAT INFORMATION DOES A PRENATAL SCREENING TEST FOR DOWN SYNDROME PROVIDE?
A screening test will tell you the chances of having a baby with a certain medical condition.
Screening tests for Down syndrome cannot tell for certain whether your baby actually has Down syndrome; rather, they can tell you whether there is a low or high chance that the baby has this condition. By comparison, a diagnostic test can tell for certain if the baby has Down syndrome.
These tests may also tell you if your pregnancy is at increased risk for certain other conditions. Some of these conditions are trisomy 18 and trisomy 13. These disorders are more life-threatening than Down syndrome.
Screening tests only require a blood sample from the mother and possibly an ultrasound, so there is no increase in risk of losing the pregnancy. Diagnostic tests for Down syndrome and other chromosome problems require putting a needle into the uterus or placenta and removing some fluid or tissue. There is a small increase in risk of losing the pregnancy (approximately 1/200 for chorionic villus sampling [CVS] and 1/300 to 1/600 for amniocentesis).
The decision to have a prenatal screening test for Down syndrome is yours and depends upon your wishes, values, and beliefs. There is no right or wrong choice. You can decide what is best for you and your family. Some couples who have a positive screening test decide against having a confirmatory diagnostic test. Others decide to continue the pregnancy even when Down syndrome is diagnosed. Testing can also be done after birth by doing a blood test on the baby.
WHO IS OFFERED A SCREENING TEST FOR DOWN SYNDROME?
The American College of Obstetricians and Gynecologists recommends that all pregnant women, regardless of age, be offered the opportunity to have a screening test for Down syndrome before 20 weeks of pregnancy. Screening tests for Down syndrome are voluntary. This means that it is your choice whether to have or not have these tests.
DECIDING TO HAVE A SCREENING TEST FOR DOWN SYNDROME
Why should I have a screening test? — These are some of the reasons that women choose to have a screening test for Down syndrome:
●I want as much information as possible about the health of my developing baby.
●If my baby has Down syndrome, I want to know while I am pregnant. Then I can learn as much as possible about the condition before birth.
●I am planning to deliver my baby in a community hospital. If my baby has serious birth defects associated with Down syndrome (such as heart or intestinal problems), I would rather deliver at a hospital with a special care nursery.
●I have been anxious since I learned I was pregnant. If I find out that my baby's chances of having Down syndrome are low, I believe it will help ease my anxiety.
●I want to consider all of my options. If my developing baby has Down syndrome, I would want the option to terminate the pregnancy.
●I am not sure what I would do, or how I would feel, if my baby has Down syndrome. I am going to take it one step at a time. If my screening test shows that the baby is at increased risk, I will decide at that time if I want to have more testing.
Why might I choose not to have a screening test? — These are some of the reasons that a woman might choose NOT to have a screening test:
●I have decided that "whatever will be, will be," and I will wait until the baby's birth to find out if the baby has Down syndrome.
●I do not want to be faced with decisions about my unborn baby. Because of religious or personal beliefs, I would never consider terminating an affected pregnancy.
●Because I am certain I would never have a diagnostic test, even with only a small increased risk of a miscarriage, I do not want to have a screening test.
●I want to know for sure if the developing baby has Down syndrome, so I am having a diagnostic test (eg, chorionic villus sampling [CVS] or amniocentesis) rather than a screening test. (See "Patient education: Chorionic villus sampling (Beyond the Basics)" and "Patient education: Amniocentesis (Beyond the Basics)".)
Some common myths about screening for Down syndrome — Some of the reasons women decide whether or not to have screening are based on incorrect information, such as:
●Myth – My baby won't have Down syndrome because I am young, I exercise, and I am healthy.
●Fact – A woman of any age can have a baby with Down syndrome, regardless of her health.
●Myth – My baby won't have Down syndrome because I do not drink or smoke.
●Fact – Avoiding alcohol or tobacco during pregnancy is very important for the health of you and your baby. However, it does not change the chance that your baby will have Down syndrome.
●Myth – My baby won't have Down syndrome because no one in my family or the father of the baby's family has Down syndrome.
●Fact – Down syndrome usually does not run in families. Your baby can be affected even if there is no one else in the family with Down syndrome. If you do have a family history of Down syndrome, you should talk to your doctor, nurse, or a genetic counselor. They can discuss if your history will increase your risk of having a baby with Down syndrome.
●Myth – I should not have screening for Down syndrome unless I know that I would terminate the pregnancy if Down syndrome were detected.
●Fact – Many people who would not terminate their pregnancy choose to have screening. These people want information about their unborn baby's health before birth to plan for delivery and newborn care.
●Myth – My friend told me that if I have a screening test, it will come back "positive" since most people who have the test end up with a "positive" result.
●Fact – Most people who have a screening test will have a "negative" result, meaning that the baby has a low risk of having Down syndrome.
WHAT DOWN SYNDROME SCREENING TESTS ARE AVAILABLE?
There are several different screening tests available. Some important considerations include:
●How far along in pregnancy are you?
●What screening tests are available in your area?
●What diagnostic tests (chorionic villus sampling [CVS] or amniocentesis) are available in your area?
There are four basic types of screening tests for Down syndrome. Some of these tests need to be done early in the pregnancy, while one is not done until 15 to 18 weeks of pregnancy (at around four months).
●First-trimester serum screening is typically done at 11 to 13 weeks of pregnancy. It involves a test of your blood and an ultrasound of the developing baby.
●Second-trimester serum screening is typically done at 15 to 18 weeks of pregnancy. The test only requires a sample of your blood.
●Integrated serum screening combines results from tests done during the first and second trimesters. These tests involve two samples of your blood and often include an ultrasound of the developing baby. Results are usually available in the second trimester.
●The newest screening method is the measurement of circulating cell-free DNA (cfDNA) in your blood. This test can be done beginning at 10 or 11 weeks of pregnancy. This test requires a sample of your blood. It cannot provide a result for some women (1 to 5 percent).
The cfDNA screening may not be paid for by your health insurance unless you are at high risk before having the test. Women at high risk are those older than 35 years of age or who have been screen positive on a serum test, or have a family history of Down syndrome or similar problems.
Which screening test should I choose? — The "best" screening test depends upon your values and preferences. You can use the following statements to help guide your decision (table 1).
TEST RESULTS
The screening test results may be described as negative/low risk or positive/high risk and a number describing your risk may be given:
●Screen negative (low risk) – For example, a woman with a result of 1 in 2000 would have a "low" risk that the baby has Down syndrome. The "1" in 2000 means that if 2000 women had this same risk, only one of them would actually have a developing baby with Down syndrome.
●Screen positive (high risk) – A woman with a result of 1 in 50 would have a "high" risk. The "1" in 50 means that, among 50 women with this same risk, one of them would have a developing baby with Down syndrome.
There is no screening result that will tell for sure if the developing baby definitely does or does not have Down syndrome.
Screen positive results — If your test shows a "high" risk of having a baby with Down syndrome, your options are:
●To have a diagnostic procedure. This would tell you for sure if your baby has Down syndrome.
●If you had one of the standard serum screening tests, you can have a cell-free DNA test for secondary screening. This test provides a more reliable result. If it finds a "low risk" result, there is no need for a diagnostic test. In a few women, it will be a "high risk" result, and you would be offered diagnostic testing (algorithm 1).
●No further testing during pregnancy. If needed, the infant can be tested after birth.
To help you with your decision, consider meeting with a genetic counselor. He or she can help answer your questions. Then, you can balance the risks and benefits of diagnostic testing and explore your feelings about raising a child with Down syndrome.
Two diagnostic procedures are available that can tell you for certain if your baby has a chromosome problem:
●Chorionic villus sampling (CVS) – CVS is the diagnostic test that would be done if you were in the first trimester of pregnancy (11 to 13 weeks). The test has a small risk of miscarriage (approximately 1 miscarriage for every 200 procedures). (See "Patient education: Chorionic villus sampling (Beyond the Basics)".)
●Amniocentesis – Amniocentesis is the diagnostic test that would be done if you were in your second trimester (after 14 weeks of pregnancy). Amniocentesis is thought to have a smaller risk of miscarriage (1 miscarriage in every 300 to 600 procedures). (See "Patient education: Amniocentesis (Beyond the Basics)".)
Where to get more information?
Your health care provider is the best source of information for questions and concerns related to your medical problem.
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