What is Amniocentesis and Do I Need One if I’m Pregnant?

Amniocentesis is an invasive medical procedure done during pregnancy.

Fetuses grow in the uterus, specifically in the amniotic sac, which is filled with a liquid called amniotic fluid. The amniotic fluid surrounds the fetus as it grows, and it also allows the fetus to move and breathe.

During amniocentesis, the doctor uses a needle to take a sample of amniotic fluid to study it for signs of birth defects.¹

Amniocentesis is usually used to diagnose genetic birth defects. This means it can be useful if you have a high risk of having a child with a genetic condition. You might be at high risk if you:²

• Were pregnant with other children with genetic conditions
• Have a family history of genetic birth defects
• Are 35 or older
• Have had a screening test that indicates high risk of a genetic condition
• Have had ultrasounds indicating potential genetic conditions

Not all pregnancies require an amniocentesis, but your doctor could recommend one if you meet one or more of these risk factors.

Why is Amniocentesis Performed?

Amniocentesis is usually performed to diagnose genetic disorders. The common genetic conditions that it tests for are:³

• Down syndrome
• Edward syndrome
• Patau syndrome

Healthy humans have two copies of each chromosome. People with three copies of certain chromosomes have these conditions.

Because amniotic fluid contains bits of the fetus’ DNA, amniocentesis allows a doctor to look at fetal DNA in the fluid to see how many of each chromosome the fetus has.³

Amniocentesis can also diagnose cystic fibrosis, neural tube defects, and other genetic conditions.^1,2

Common Indications for Amniocentesis

Amniocentesis is a versatile procedure and can be performed for many different reasons. Some of the most common ones are:¹

• Diagnosing chromosomal conditions like Down Syndrome
• Diagnosing other genetic conditions like neural tube defects
• Diagnosing infections in the fetus 
• Diagnosing infections in the amniotic fluid and placenta
• Determining fetal lung maturity (Note: It is important to test for fetal lung maturity if your baby needs to be delivered early)
• Diagnosing Rh disease⁴

When is the Best Time for Amniocentesis?

You should wait until at least week 15 of your pregnancy to have an amniocentesis. 

Before 15 weeks of pregnancy, there is a greater risk of complications.¹ Usually, the procedure is performed between 15 and 20 weeks of pregnancy.³

How is Amniocentesis Performed?

Amniocentesis is an outpatient procedure, meaning you will not need to stay at the hospital overnight when you have one. The steps involved in amniocentesis are the following:¹

• Before the procedure, the doctor will perform an ultrasound to determine the position of the fetus and placenta
• The doctor will disinfect your skin and begin another ultrasound to monitor the procedure
• They will insert a syringe into your abdomen and through to the amniotic sac, possibly causing some discomfort or pain³
• The ultrasound will help the doctor ensure the needle does not come into contact with the fetus or the placenta
• The doctor will use the syringe to take an amniotic fluid sample and remove the needle
• The amount of amniotic fluid taken will depend on the conditions the doctor will test for
• After the fluid is drawn, the doctor will check the fetus’ heartbeat and movement to ensure its condition is normal

Is Amniocentesis Safe for the Baby?

Amniocentesis is generally considered to be a safe procedure. However, remember that any medical procedure will have risks associated with it.

There is a low risk of miscarriage as a result of amniocentesis. This risk can be less than 1% if you have no other risk factors for miscarriage.

Some diseases, like HIV, can be transferred from the parent to the child during amniocentesis. If you have HIV, you should start taking antiretroviral drugs before undergoing amniocentesis. Reducing the viral load through medication makes the risk of transmission to the fetus much lower.

If you are taking blood thinners, you should stop taking them for two to three days before the procedure. Your doctor might need to temporarily alter your prescription if you take blood thinners and require amniocentesis.¹

Risks of Amniocentesis

Other possible complications of amniocentesis include:⁴

• Bleeding
• Cramps
• Amniotic fluid leaking from the vagina or the abdomen where the needle was used
• Infections
• Preterm labor

What if Amniocentesis Results are Positive?

Positive amniocentesis results mean your child will be born with a genetic or chromosomal condition. 

Usually, this indicates Down Syndrome, Edward Syndrome, or Patau Syndrome. These are all conditions caused by extra copies of certain chromosomes.¹

While receiving positive amniocentesis results can be difficult, it can also prompt early meetings with relevant experts. Disability experts, geneticists, and others can help you interpret your results, what they mean for you and your child, and how to best manage the pregnancy going forward.

This can mean making arrangements to properly accommodate the child or the decision to terminate the pregnancy.^1,3

Amniocentesis vs. Other Prenatal Tests

Amniocentesis is just one of many possible prenatal tests that can tell you more about the fetus's health. Chronic villus sampling (CVS) and non-invasive prenatal testing (NIPT) are also commonly performed.

Amniocentesis vs. chronic villus sampling

Like amniocentesis, CVS is an invasive test that can diagnose genetic conditions. 

Instead of taking a sample of the amniotic fluid, CVS involves taking a sample of the placenta, also located in the amniotic sac. 

CVS tests for similar genetic conditions as amniocentesis but can be performed earlier. While amniocentesis is done during week 15 of the pregnancy at the earliest, CVS is usually performed from 11 to 14 weeks. 

CVS can be performed by piercing the abdomen with a needle line in amniocentesis. It can also be performed by inserting a tube through the cervix.⁵

Amniocentesis vs. non-invasive prenatal testing

Unlike amniocentesis, NIPT is a non-invasive test. 

Instead of examining the amniotic fluid, NIPT only requires taking a sample of your (the mother’s) blood. When you are pregnant, your blood will contain bits of DNA from the fetus, which can be analyzed. This can tell you about potential genetic disorders.⁶

Amniocentesis is a diagnostic test, which means that it can tell you whether or not the fetus has a particular condition. In contrast, NIPT is a screening test, which can only tell you about the risk the fetus will be affected by a condition.

Instead of a positive or negative result, NIPT can tell you if the fetus has an increased risk of being affected by a genetic disease. A high-risk result does not mean a genetic disorder is certain and will require further testing to confirm.^6,7

Why Amniocentesis is Better Than Ultrasound

Ultrasound is essential for monitoring the health of the fetus during pregnancy. It can even detect potential genetic disorders by looking at the amount of fluid behind the neck of the fetus. 

However, when it comes to genetic disorders like Down syndrome, ultrasound findings are not definitive. Further tests like amniocentesis will be necessary to truly diagnose the condition.^8,9

How Accurate is Amniocentesis for Down Syndrome?

Amniocentesis is extremely accurate when it comes to diagnosing Down Syndrome. An amniocentesis result will be accurate almost 100% of the time. However, not all genetic disorders can be detected by amniocentesis.¹

How Much Does Amniocentesis Cost?

Amniocentesis can cost around $4,000. However, this price can vary greatly depending on your location and insurance coverage.¹⁰

Recovery and Post-Procedure Care

After amniocentesis, you will be monitored for some time.

When recovering from an amniocentesis, you can experience some cramping, similar to menstrual cramps, and light vaginal bleeding or spotting. These are normal and should resolve a few hours after the procedure.

You can take paracetamol to help with the pain, but ibuprofen or aspirin should be avoided.³

After amniocentesis, keep an eye out for vaginal bleeding, severe pain, fever, or leaking vaginal fluid, as amniotic fluid can leak from the vagina after amniocentesis. If you experience any of these, be sure to consult your doctor.¹

Do I Need Bed Rest After Amniocentesis?

No, bed rest is not necessary after amniocentesis. Generally, you should be able to go about your day as normal, but it is best to avoid strenuous physical activity for the rest of your day after the procedure.¹