Should I have an amniocentesis?
Introduction
This information will help you understand your choices, whether you share in the decision-making process or rely on your doctor's or registered midwife's recommendation.
Key points in making your decision
This information will be helpful if you are trying to decide whether to have a diagnostic amniocentesis to test for certain types of fetal problems.
Consider the following when making your decision.
- Amniocentesis is not a routine test because it does carry a small risk of miscarriage (about 1 in 400).1 Your decision lies in weighing the slight risk of miscarriage from amniocentesis against the information the testing can provide.
- An amniocentesis can accurately detect many birth defects including Down syndrome, but it cannot rule out all problems or guarantee your baby will be free of all birth defects.
- Knowing how you might handle news of a birth defect can help you decide whether to have an amniocentesis. If you would consider terminating a pregnancy with a serious birth defect, an amniocentesis is a useful test. If advance notice would help you cope with a sick, disabled, or dying newborn, an amniocentesis may also be useful for you. With early test results, you can also plan ahead to deliver in a specialized hospital, if needed.
- Results from an amniocentesis may not be available until about 18 weeks of pregnancy. For some women who would consider terminating a pregnancy involving a birth defect, this may be too late in a pregnancy to do so. If this is the case for you, talk to your health professional about earlier testing, such as chorionic villus sampling.
Medical Information
What is an amniocentesis?
Amniocentesis is a procedure used to take a small sample of the amniotic fluid that surrounds a fetus. Amniotic fluid contains cells and waste products from the fetus that can give clues about the fetus's health. The procedure is done by inserting a needle through your abdomen into the uterus. Approximately 30 mL (2 Tbsp) of the amniotic fluid is drawn out and then tested in a laboratory. Amniocentesis is done between weeks 15 and 20 (usually around week 16) of pregnancy.
Genetic testing of the amniotic fluid sample can detect fetal genetic problems, including more than 100 types of inherited diseases (such as cystic fibrosis, sickle cell disease, and Huntington's disease), Down syndrome, and neural tube defects. A fetus's sex can also be identified by testing the amniotic fluid.
How would I use amniocentesis results?
Normal results from an amniocentesis suggest that a fetus has normal chromosomal formation and no markers for neural tube defects. Although this is reassuring, it does not guarantee that a baby will be born completely healthy—no single test can find all possible problems.
If abnormal test results tell you that your fetus has a birth defect, you can make informed, if difficult, decisions. The decisions you are faced with depend on various factors. These include the specific type of defect involved and your own and your partner's preferences. For example, you may want to consider:
- Whether to continue the pregnancy. If a fetus has a severe defect, some women choose to end the pregnancy (have a therapeutic abortion). Others want time to prepare themselves and their families for the birth of a child who has a birth defect.
- Where to have the baby. If the fetus has a defect that will require surgery, it is best to deliver at a hospital that offers surgical services for newborns.
- Whether to have a vaginal delivery or to plan a caesarean delivery (C-section), based on the fetus's condition.
Is there another type of test I can have instead of amniocentesis?
If you are still in your first trimester, you can consider chorionic villus sampling (CVS) as an alternative to amniocentesis. CVS can detect Down syndrome and genetic diseases earlier in pregnancy than amniocentesis. However, CVS cannot detect a neural tube defect.
A recent study showed that both tests have about the same risk of miscarriage. In that study, the miscarriage risk was about 1 in 400, with the tests being done by highly trained providers.1 Some studies have shown higher miscarriage risks, between 2 and 4 in 400. This greater risk may be more likely in medical centres with less experienced providers, especially for CVS.2 The CVS risk may be less when it is done through the abdomen rather than through the cervix.3 For more information, see the medical test Chorionic Villus Sampling.
What are the risks of amniocentesis?
Amniocentesis is usually very safe. In a pregnancy for which amniocentesis is recommended, the benefit of knowing whether the fetus has a birth defect, inherited disease, or Down syndrome is typically greater than the risk of having the procedure. However, there are some risks, including:
- Injury to the mother or fetus from the needle. Using ultrasound to guide the needle reduces this risk. The most common injury is puncture of the placenta, which usually heals without a problem.
- A less than 1 in 1,000 risk of causing an infection by introducing bacteria into the amniotic sac.4
- Miscarriage. About 1 of every 400 amniocentesis procedures is linked to miscarriage.1 (Some miscarriages after amniocentesis are not linked to the procedure. Instead, they are caused by a problem with the fetus or pregnancy.)
- A slight risk that the mother will be exposed to the fetus's blood during amniocentesis. This is only a concern if your blood is Rh-negative and you are at risk of Rh sensitization. If so, sensitization can be prevented with a vaccine given after the test.
- An increased risk that the fetus will develop club foot
when testing before 15 weeks of pregnancy.
What are the risks of not having an amniocentesis when one is recommended?
If you don't have prenatal diagnostic testing, you could potentially give birth to a baby with an undiagnosed birth defect or Down syndrome.
- Such a birth can be more complicated and risky to the baby when a doctor is not expecting newborn health problems.
- You could give birth in a hospital that does not have a neonatal intensive care unit (NICU) for sick newborns.
- A fetus with a very rare, severe defect sometimes dies before delivery.
- Many parents are emotionally ill-prepared for the sudden birth of a Down syndrome or sick baby.
Talk to your health professional about all available testing options. You may be able to rule out a genetic condition with another, less invasive test.
Should I consider an amniocentesis at all?
Amniocentesis is not used for routine early pregnancy screening because it carries some risks. It is done when the risk of a defect or disease outweighs the risks of the procedure. A doctor's recommendation is based on family history, your age, or results of screening tests such as the triple or quadruple screen test.
Amniocentesis is a reasonable choice for you to consider if your fetus has an increased risk of a birth defect or genetic problem. Common reasons for electing to have an amniocentesis include:
- Abnormal results from a maternal serum triple screen or alpha-fetoprotein test, suggesting that your fetus may have a birth defect or Down syndrome.
- Fetal ultrasound imaging suggesting the presence of a birth defect.
- Maternal age of 35 or older. As you age, you have a progressively increasing risk of having a child with Down syndrome. In mothers who are 35, about 1 baby in 350 is born with Down syndrome. By age 40, about 1 baby in 100 is born with Down syndrome.5
- Family history of birth defects, such as a neural tube defect.
- Parent (you or your partner) who is a carrier of an inherited disease, such as Tay-Sachs disease or sickle cell disease.
- A need to know the fetus's sex. This is important when a parent is a carrier of a sex-specific disease, like hemophilia or Duchenne muscular dystrophy. Both of these diseases occur mainly in males.
You may also consider an amniocentesis if you have repeatedly miscarried after the first trimester, to screen for a preventable cause.
For more information, see the medical test Fetal Ultrasound. For more information about the triple screen, see:
- Maternal serum triple or quadruple screen.
- Alpha-Fetoprotein in Blood.
- Human Chorionic Gonadotropin (hCG).
- Estrogens.
- Hormone Inhibin A.
Your Information
Your choices are:
- Have an amniocentesis.
- Do not have an amniocentesis.
The decision about whether to have an amniocentesis takes into account your personal feelings and the medical facts.
Making a decision about amniocentesis Reasons to have an amniocentesis Reasons not to have an amniocentesis
- Your triple or quadruple screen test and fetal ultrasound results suggest an increased risk of fetal problems.
- You will be age 35 or older on your due date.
- You or your partner has a family history of birth defects that can be detected with amniocentesis.
- You or your partner is a carrier of a genetic disease.
- You have had repeated miscarriages after the first trimester.
Are there other reasons you might want to have an amniocentesis?
- You are concerned about the 1-in-400 rate of miscarriage following amniocentesis procedures.1
- You are concerned about the less than 1-in-1,000 risk of infection.4
- Your triple or quadruple screen test and fetal ultrasound results do not suggest an increased risk of fetal problems.
- You have no risk factors for birth defects or Down syndrome.
- Knowing about a fetal problem ahead of time would not change your medical, birthing, or parenting plans.
Are there other reasons you might not want to have an amniocentesis?
These personal stories may help you make your decision.
Wise Health Decision
Use this worksheet to help you make your decision. After completing it, you should have a better idea of how you feel about amniocentesis. Discuss the worksheet with your health professional.
Circle the answer that best applies to you.
I will be age 35 or older on my due date. Yes No Unsure I have a risk factor for a fetal genetic disorder. Yes No Unsure I am still in my first trimester, have a risk factor, and am considering chorionic villus sampling for an earlier diagnosis than amniocentesis can give me. Yes No Unsure My triple screen results point to a possible fetal problem. Yes No Unsure My fetal ultrasound points to a possible fetal problem. Yes No Unsure I have explored any other possible tests that could confirm or disprove the possibility of a fetal problem. Yes No Unsure Knowing about a severe fetal problem would not change my plans to carry to term. Yes No Unsure I am concerned about miscarriage risk. Yes No Unsure I am concerned about infection risk. Yes No Unsure I need as much diagnostic information as possible to alleviate my concerns about my baby. Yes No Unsure Use the following space to list any other important concerns you have about this decision.
What is your overall impression?
Your answers in the above worksheet are meant to give you a general idea of where you stand on this decision. You may have one overriding reason to have or not have an amniocentesis.
Check the box below that represents your overall impression about your decision.
Leaning toward having an amniocentesis
Leaning toward NOT having an amniocentesis
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| Author: | Shannon Erstad, MBA/MPH | Last Updated: January 23, 2008 |
| Medical Review: | Renée M. Crichlow, MD - Family Medicine Kirtly Jones, MD - Obstetrics and Gynecology | |
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