Amniocentesis: What to Expect

An amniocentesis test is a prenatal procedure, which can diagnose certain health conditions in the fetus.

Your healthcare provider may offer you this test during your pregnancy. Usually, it’s because of the risk for genetic disorders or neural tube defects. An amniocentesis carries some risks, and while many expectant parents have this test, others decide against it. 

This article walks you through the procedure and purpose of amniocentesis, what to expect before, during, and after the test, and what the results mean.

What Is Amniocentesis?

To perform an amniocentesis, a healthcare provider takes a small sample of amniotic fluid for testing. The fluid contains cells and substances that provide clues to fetal health.

Results are quite accurate. Your healthcare provider or obstetrician may recommend an amniocentesis if prenatal screenings suggest certain genetic conditions or birth defects.

What Is Amniotic Fluid?

Amniotic fluid is the liquid surrounding the fetus. It’s inside a membrane called the amniotic sac.

When your “water breaks,” it’s the sac rupturing and releasing the amniotic fluid. The fluid is clear and slightly yellowish. It serves many purposes, including:

• It keeps the temperature constant.
• It provides cushioning for the fetus.
• It helps with fetal lung development, flowing in and out of the mouth and lungs.
• It allows the fetus to move, which helps with bone growth.

Purpose of an Amniocentesis Test

Amniocentesis can diagnose many health problems. These include:

• Genetic disorders: Conditions caused by genetic mutations, such as cystic fibrosis, Tay-Sachs disease, and fragile X syndrome
• Chromosomal disorders: Conditions caused by abnormal, missing, or extra chromosomes (genetic material), such as Down syndrome, learning disabilities, or other health problems
• Neural tube defects: Abnormal development of the fetal spine and/or brain

Amniocentesis can also identify prenatal infections, gauge fetal lung development, and determine your baby's sex before birth. Some parents want to know this information before the birth for several reasons:

• Emotionally and logistically preparing for a special-needs baby
• Easing fears about possible genetic diseases
• Getting a realistic view of development in a baby at risk for premature birth
• Deciding whether to terminate the pregnancy

Who’s a Good Candidate?

Your healthcare provider may recommend amniocentesis if they think you’re a good candidate for it. Their criteria may include:

• Other tests that suggest a high risk of birth defects
• A history of birth defects in your family or your partner’s
• Either parent carries an abnormal gene linked to disease
• There's a risk of a sex-related disease
• You’re over 35 

An amniocentesis for those reasons is usually done in the second trimester. It may be recommended for the third trimester if: 

• There is a risk of premature birth (to check lung development) 
• Uterine infection
• Rh disease 

What to Expect

Second-trimester amniocentesis is generally done between the 15th and 20th weeks of your pregnancy. The test itself only takes about 15 minutes.

Before the Test

You’ll be told whether to have a full or empty bladder. The later the test is done in pregnancy, the more likely it is you’ll need an empty bladder.

Ask your healthcare provider or the testing facility if you need to do anything else to prepare. Check with your insurance so you know whether the test is covered and how much you’ll need to pay.

On the day of the test, wear clothes that are easy to remove. Leave jewelry and other valuables at home. Be sure you have your insurance card and a co-pay, if needed. Arrive early enough to get checked in before your amniocentesis procedure’s scheduled time.

During the Test

For the test, you’ll lie on your back. The healthcare provider will use an ultrasound to see where your baby is and identify a good insertion point. 

They may put numbing medication on the insertion point. They’ll then use a small needle to withdraw some fluid. Once they have the sample, they’ll continue the ultrasound to monitor the fetal heartbeat.

You may have some mild discomfort or cramping during or after the procedure. This is normal. Tell the healthcare provider if you have concerns at any time.

After the Test

You’ll stay at the office or testing facility for about an hour afterward. This is so they can monitor both you and the fetus. Tell someone if you feel dizzy or nauseated. 

Once you’re released, it’s best to go home and rest. Don’t do anything strenuous for about 24 hours afterward. If you have lingering discomfort, ask your healthcare provider if you can take any medicine for it. Other reasons to contact your healthcare provider include:

• Bleeding or amniotic fluid leaking from the vagina or needle insertion site
• Severe belly pain or cramping
• Fever or chills
• Changes in fetal activity levels

What Do the Test Results Mean?

Ask your healthcare provider when you should expect the results of your amniocentesis. It may take a few days or weeks.

A positive result means the test found a genetic abnormality or other problem. You may be contacted by your healthcare provider, a genetic counselor, or a specialist in obstetrical genetics.

They’ll go over the results with you so you understand what they mean. You may have decisions to make regarding treatments or other actions based on the results.

How Accurate Is an Amniocentesis?

Amniocentesis is extremely accurate. In fact, it’s close to 100%.

It can detect many health conditions but not all of them. So a negative amniocentesis can’t guarantee your baby will be born healthy. It only looks for very specific conditions and problems.

What Can’t an Amniocentesis Test Detect?

Amniocentesis can’t detect all birth defects and health problems. 

For example, it won’t find structural issues such as a heart problem, cleft lip, or cleft palate. However, ultrasound can detect many structural defects.

Some preliminary research suggested an amniocentesis may be able to detect autism spectrum disorders (ASD) based on testosterone levels. However, further studies have had mixed results. So, for now, this test isn’t used to diagnose ASDs.

Risks of Amniocentesis

Amniocentesis comes with some risks. These include:

• Cramping
• Bleeding/amniotic fluid leaking from the vagina or puncture site
• Infection
• Preterm labor
• Miscarriage

The risk of miscarriage after a second-trimester amniocentesis is less than 1%. It’s a slight increase over the normal risk.

The risk is higher before the 18th week of pregnancy. Many healthcare providers won’t perform this test before then.

You may face additional risks depending on your health or other factors.

Summary

Amniocentesis is a highly accurate test. It involves withdrawing amniotic fluid and testing it for genetic conditions and other problems. It's also used to determine sex and lung development.

A positive result means the test found something. Your healthcare provider can explain what that means.

The test slightly increases your risk of certain complications, such as miscarriage and preterm labor. Report any signs to your healthcare provider right away.

A Word From Verywell

If your healthcare provider recommends an amniocentesis, you need to make the decision to have or not have the test. It’s up to you.

You may decide the minimal risk is worth it for peace of mind or to give you time to prepare. On the other hand, you may decide the test isn’t worth it because it wouldn’t change anything about your pregnancy or preparations.

Rest assured that many parents have faced similar decisions. It’s a very personal, individual choice that you should make with your family and healthcare team.