Amniocentesis: What to Expect

An amniocentesis test is a prenatal procedure, which can diagnose certain health conditions in an unborn baby. 

Your healthcare provider may offer you this test during your pregnancy. Usually, it’s because your baby is at 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 for you and your baby.

Pregnant woman

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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 give clues to the baby’s health.

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

Amniocentesis can also tell your baby’s sex, identify prenatal infections, and gauge lung development.

What Is Amniotic Fluid?

Amniotic fluid is the liquid surrounding your baby. 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 your baby.
  • It flows in and out of your baby’s mouth and lungs, helping with lung development.
  • It allows the baby to move, which helps with bone growth.

Purpose of an Amniocentesis Test

Amniocentesis can diagnose many health problems. These include:

Amniocentesis can also tell your baby’s sex, identify prenatal infections, and gauge lung development. 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

Questions to Ask Your Healthcare Provider

  • What are the odds you’ve passed a genetic disease to your baby?
  • How high is your baby’s birth defect risk?
  • What can be done if something comes back positive?
  • What’s the risk of a false positive?
  • What risks come with an amniocentesis?
  • How should you prepare for the test?
  • When will the results come back?


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
  • Your baby is at risk for 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: 

  • Your baby is at risk for premature birth (to check lung development) 
  • Uterine infection
  • Rh disease 

What Is Rh Disease?

Rh disease is possible when the Rh factor in your blood is negative (A-, B-, O-, or AB-) and the baby’s is positive. Your immune system may identify the baby’s blood as a threat and try to destroy it.

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 the 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 baby’s 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 you and the baby. 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 your baby’s 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:

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.

Signs of Miscarriage After Amniocentesis

  • Vaginal spotting
  • Abdominal pain or cramping
  • Fluid or tissues coming from your vagina

Contact your healthcare provider any time you have vaginal bleeding during pregnancy.

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.

Pros
  • Can put your mind at ease

  • Allows time to prepare for a special-needs child

  • More accurate than screening tests

Cons
  • Time consuming

  • May be expensive (depending on your insurance)

  • Slight risk of miscarriage or early labor

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 made the same decision as you. It’s a very personal, individual choice that you should make with your family and healthcare team.

Frequently Asked Questions

  • How painful is an amniocentesis?

    It’s not usually painful. You might be uncomfortable during the test. Afterward, you may have cramping similar to a period. If you’re worried about the amniocentesis needle hurting, ask if your belly will be numbed before the needle is inserted.

  • How much does an amniocentesis cost?

    Costs for amniocentesis range from a few hundred dollars to several thousand. It depends on where you have it done. Insurance often pays for all or most of the test. Be sure to check on this before the test so you don’t get surprised when the bill comes.

  • Can I choose not to have an amniocentesis?

    Yes, choosing not to have amniocentesis is a valid option. This is a very personal decision that should be made by you and your partner or family along with your healthcare provider.

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6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. MedlinePlus. Amniotic fluid.

  2. University of Michigan Health, Michigan Medicine. Pregnancy: should I have amniocentesis?

  3. Stanford Children’s Health, Lucile Packard Children’s Hospital. Rh disease.

  4. University of California San Francisco Health. Amniocentesis FAQ.

  5. Cleveland Clinic. Genetic amniocentesis.

  6. Kung KT, Spencer D, Pasterski V, et al. No relationship between prenatal androgen exposure and autistic traits: convergent evidence from studies of children with congenital adrenal hyperplasia and of amniotic testosterone concentrations in typically developing children. J Child Psychol Psychiatry. 2016;57(12):1455-1462. doi:10.1111/jcpp.12602

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