What Is Amniocentesis?

Amniocentesis (or amnio) is a medical procedure used for the prenatal diagnosis of chromosomal abnormalities and other fetal medical conditions. The screening test is done using a long needle that's inserted through the mother's abdomen to collect a sample of amniotic fluid. It is often recommended for women who are over the age of 35 or who have risk factors for having a baby with a genetic condition.

The procedure is usually done between 15 and 20 weeks gestation and carries some potential risks, including miscarriage. However, the rate of complications is very low. Potential benefits of the procedure include the opportunity for parents to plan for a special needs child, to initiate in utero treatment (if applicable), and make a more educated decision about whether or not to continue a pregnancy.

Why It's Important

The American College of Obstetricians and Gynecologists (ACOG) recommends genetic screening be offered to all pregnant women, either via less invasive prenatal tests (like blood tests) or through more invasive tests such as amniocentesis or chorionic villus sampling (CVS). Consider your doctor's recommendations and your risk factors as you decide whether or not to have an amniocentesis.

Uses

Your doctor may recommend amniocentesis for a number of reasons, such as your age, family medical history, and/or an abnormal screening test. (Note that a positive screening test means that there is an increased risk of chromosomal abnormalities, not that a definitive abnormality has been found.) Some specific reasons why an amniocentesis may be recommended include:

• Abnormal results on a first-trimester or second-trimester ultrasound
• Abnormal results on prenatal blood screening tests, such as a quad screen or prenatal cell-free DNA screening
• Family history of certain genetic conditions (you or your partner)
• Lung maturity testing
• Maternal age of 35 or older: The risk of chromosomal abnormalities increases significantly with age, especially after the age of 35. (Keep in mind that most babies born to mothers of advanced maternal age, even over the age of 40, do not have chromosomal abnormalities)
• Polyhydramnios (too much fluid in the uterus): If too much fluid is present, an amniocentesis may be done to remove the excess liquid
• Previous child with a chromosomal abnormality or neural tube defect
• Suspected uterine infection
• To evaluate Rh disease
• To deliver medications into the uterus

Conditions Detected

Conditions that may be detected with an amniocentesis include:

• Chromosomal abnormalities, such as Down syndrome (see other examples below)
• Congenital infections that can cause birth defects, such as cytomegalovirus, herpes, rubella (German measles), toxoplasmosis, parvovirus B19, and Zika virus
• Genetic conditions, such as sickle cell disease and cystic fibrosis
• Neural tube defects, including spina bifida or anencephaly

Potential Benefits

There are many reasons why some women choose to have an amniocentesis, including peace of mind. It's important to note that, like all prenatal testing, choosing an amniocentesis is optional and completely up to the discretion of the pregnant mother. Below are some potential benefits of the test, each of which may be valued differently by individual pregnant women:

• Give parents information that may factor into considering termination of pregnancy (also called therapeutic termination) when birth defects will be incompatible with life or reduce the quality of life for the fetus
• Help parents cope with and better prepare physically and/or emotionally for a special needs child
• Lead to an earlier diagnosis, so that treatment may be started before birth (for example, stem cell treatments in fetuses with sickle cell disease)

Potential Limitations

While amniocentesis is a very accurate test for detecting chromosomal problems, it cannot diagnose all potential genetic problems or birth defects in a fetus. So, while a normal amniocentesis is a good indicator that you will have a healthy baby, it is not a guarantee. Plus, you'll need to weigh the small chance of miscarriage or other complications against the benefits of the information this test provides.

Other Testing Options

In addition to amniocentesis, there are other testing options to screen for chromosomal abnormalities and other health concerns with your baby. These include the following:

Chorionic Villus Sampling

A similar test for evaluating chromosomal abnormalities is chorionic villus sampling. CVS is also an invasive test in which a sample of the placenta (chorionic villi) is obtained via the cervix or abdominal wall between weeks 10 and 13 of pregnancy.

CVS has the advantage of being done earlier in the pregnancy (this is especially helpful if termination is a consideration), but it can't diagnose some conditions that can be discovered with amniocentesis, such as neural tube defects. This test also has a slightly increased chance of causing a miscarriage.

Other Tests

Noninvasive prenatal testing options include blood tests that can give clues to the presence of chromosomal abnormalities or neural tube defects in a fetus. However, blood tests cannot conclusively diagnose these conditions.

A Quad screen, which is often done as a part of routine prenatal care, is a screening test that looks for the combination of alpha-fetoprotein (AFP), estriol, human chorionic gonadotropin (hCG), and inhibin A. If this test shows any abnormalities, amniocentesis is often recommended.

Prenatal cell-free DNA testing is another test that can also give clues to the presence of chromosome abnormalities. Genetic testing may also include other types of tests, such as preimplantation screening and carrier screening, for example, to see if either parent-to-be carries the gene for cystic fibrosis.

Additionally, as advances take place in molecular testing, especially with the advent of tests to evaluate circulating DNA and DNA fragments, there may be less invasive methods of obtaining the same results of amniocentesis available in the future.

Risks and Contraindications

There are potential risks associated with an amniocentesis that need to be weighed against the possible benefits. Consider the emotional impact of having (or not having) an amniocentesis, which can stem from the procedure itself and/or potential results. Understand that worrying about complications can be very stressful, but not knowing can be as well.

Potential Risks

Possible complications of amniocentesis include the following:

• Amniotic fluid leak: Roughly 2% of women experience leakage of amniotic fluid after an amniocentesis, but this complication resolves on its own in the majority of cases.
• Infection: There is a small risk of infection from introducing bacteria on the skin into the uterus.
• Miscarriage: The risk of miscarriage due to amniocentesis varies based on the study, but ranges from 1 in 1000 to 1 in 200. A 2018 review of studies from 2000 to 2017 found that the overall risk of miscarriage directly related to amniocentesis was slightly more than 1 in 300 women. This risk is greater for women who have an amniocentesis before 15 weeks gestation.
• Needle injury: There is a small risk that a baby's arm, leg, or other part of the body could be penetrated by the spinal needle. This is very uncommon.
• Preterm labor: When amniocentesis is done after 20 weeks, preterm labor is a possible (but rare) complication.
• Rh sensitization: Due to exposure of the fetus to the mother's blood, there is a slim possibility that Rh sensitization from an Rh-negative mother to an Rh-positive fetus could occur. This is rare because mothers who are Rh-negative are given the medication Rhogam after the procedure to prevent this complication.
• Transmission of infections to the baby: Infections such as hepatitis B, hepatitis C, HIV, and toxoplasmosis could be transmitted from the mother's blood to the fetus during the procedure (see contraindications below).

Some research has shown a possible association between amniocentesis and clubfoot (talipes equinovarus), a birth defect in which the baby's foot is twisted due to a shortened Achilles tendon. However, more comprehensive studies have not supported this link. Instead, researchers suspect that any relationship is due to other factors rather than the amniocentesis itself.

Contraindications

There are several relative contraindications for an amniocentesis. With these conditions, an amniocentesis may be done in certain circumstances, but the risks need to be very carefully weighed against possible benefits. These include:

• Anterior placenta
• Low amount of amniotic fluid (oligohydramnios)
• Mothers who have an infection on the skin of the abdomen
• Mothers who have chronic infections with hepatitis B, hepatitis C, or HIV

Your doctor will help you in making a final determination of whether or not an amniocentesis is the best course of action for you and your baby.

Types of Genetic Testing

The specific results reported on your amniocentesis will depend on the reason the procedure was recommended for you and what tests were ordered on the sample. The type of genetic testing done will also impact the time it takes to get your results, which can vary from a few days to two weeks or longer.

A karyotype is a picture of your baby's chromosomes and is the test that takes the longest to complete. It is 99% accurate for detecting chromosomal abnormalities.

Fluorescent in situ hybridization (FISH) analysis is another test that may be done on amniotic fluid. This test is often available much more rapidly (only a few days), but it can't differentiate between the various types of Down syndrome.

Frequency of Abnormal Results

Many people wonder how often chromosomal abnormalities are found. It is estimated that between 3% and 5% of amniocentesis procedures will find a chromosomal condition. Again, it's important to note that amniocentesis cannot diagnose all birth defects or potential genetic conditions.

What the Test Detects

Ask your doctor exactly which kind of testing will be done in your amniocentesis. In general, structural chromosomal abnormalities that may be detected by amniocentesis include the following:

Additions, Deletions, Duplications, and Inversions

Chromosomal additions are when extra material is added to chromosomes. Deletions are when part of a chromosome is missing. Duplications occur if part of a chromosome is duplicated (there are two copies of one part of a chromosome) when there should only be one. When the genetic material on a chromosome is "turned around," this is called an inversion.

Monosomies

Monosomies are when there is a single copy of a chromosome pair rather than the expected two pairs. The most common monosomy is Turner syndrome (XO) in which there are only 45 chromosomes, with one of the sex chromosomes missing.

Mosaicism

Mosaicism occurs when one of the conditions above affects only some of the cells. For example, a baby may be born alive with mosaic trisomy 9, in which there are three copies of chromosome 9 in only a small percentage of cells in the body. (Full trisomy 9 is incompatible with life and usually causes an early miscarriage.)

Translocations

With translocations, the genetic material from one chromosome is attached to another chromosome. These may be balanced, which results in no gain or loss of genetic material, while an unbalanced translocation can result in either monosomy or trisomy of a chromosomal segment.

Trisomies

Normally, each person has 46 chromosomes (23 pairs), but with a trisomy, there is an extra chromosome (for a total of 47 chromosomes). Possible findings may include Down syndrome (trisomy 21, in which there are three copies of chromosome 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13).

There can also be trisomies of the sex chromosomes, such as Klinefelter's syndrome (XXY) and triple X syndrome (XXX).

Molecular Abnormalities

Molecular abnormalities, or changes in one or more genes, may also be found on an amniocentesis. Some conditions that may be diagnosed include:

• Cri-du-chat syndrome
• Cystic fibrosis
• Fragile X syndrome
• Muscular dystrophy
• Sickle cell disease
• Tay-Sachs disease
• Thalassemia

Infection Tests

If your amniocentesis was done to check for the presence of congenital infection in the baby, antibody tests will be returned as either positive or negative. A positive result means that an infection was found.

What Happens During the Test

An amniocentesis may be done in an obstetrician's office or at a medical center or hospital. During your test, there will be a few people in the room with you, including a nurse, an obstetrician, and sometimes a radiologist or radiology technician. Your partner (or another support person) may or may not be able to be in the room with you.

Timing

The amniocentesis procedure itself usually only takes about five minutes, but it's important to set aside a few hours for the procedure. This includes the time to check your vital signs, the baby's heart rate, and the fetal position before the procedure. You will also be observed for a short time after the procedure to make sure you and the baby are doing well before going home.

Pre-Test

When you talk to your doctor about having an amniocentesis, they will ask about any risk factors you may have for chromosomal abnormalities, any medical conditions you have, and any medications you are taking. Your doctor will ask you about any allergies you may have, including an allergy to latex. They will also want to review your prenatal blood tests and determine your blood type and Rh factor.

Before your procedure begins, you will be asked to sign a consent form indicating you understand the purpose of the procedure and potential risks. You may meet with a genetic counselor who will review possible results with you so that you understand what information you may learn from your test. Your nurse will check your temperature, pulse, and blood pressure, as well as your baby's heart rate.

Since the ultrasound may reveal the baby's sex, and the chromosomal analysis will for certain determine the sex, it's important to let your nurse know if you do not want to know if you're having a boy or a girl. If you want to keep this information a surprise until delivery, they can attach a note to your records so that your doctor won't inadvertently tell you when sharing your test results.

The Procedure

When you are ready for the test, you will be asked to change into a gown and lie on your back on the procedure table. Ultrasound gel will be applied to your abdomen and ultrasound will be used to determine your baby's position, the location of the placenta, and to look for pockets of amniotic fluid. This may take some time, especially if you have an anterior placenta.

Once the obstetrician has done a basic ultrasound evaluation of your baby, your abdomen will be cleaned with an antiseptic. With ultrasound guidance, a long hollow needle will then be inserted through your abdominal wall into your uterus. You may be asked to move around a bit to redistribute amniotic fluid.

When the needle is in the proper location, your doctor will withdraw roughly 20 to 30 milliliters (about 4 to 6 teaspoons) of fluid. This amount of fluid loss will not hurt your baby in any way, and your body will quickly replenish it. You may feel some discomfort and cramping as the fluid is removed. Once the fluid is retrieved, the needle is removed and a bandage is placed over the insertion site.

Post-Test

After your procedure, your nurse will continue to monitor your baby's heart rate for several minutes and will ask you about any discomfort or leakage of amniotic fluid. If you are Rh-negative, your nurse will administer a shot of Rhogam (Rh immune globulin) to prevent your baby from developing Rh sensitization.

When your test is done, you will be allowed to return home. Your doctor will let you know roughly how long it will be until results are available. Women are usually advised to avoid strenuous activity for several days and to abstain from sexual activity for a day or two.

Managing Side Effects

Some cramping is normal for the first couple of hours after the procedure, but roughly 1% to 2% of women experience more cramping and spotting that can raise a concern about impending miscarriage. However, even when these symptoms occur, most people do not go on to miscarry.

Call your doctor if you experience any significant cramping, abdominal pain, or contractions, as well as any vaginal bleeding. It's also important to seek medical attention if you develop a fever or chills, suspect you are leaking amniotic fluid, or notice a change in your baby's activity (either increased or decreased movement) if you are far enough along to feel these movements.

Genetic Counseling

You may wish to speak with a genetic counselor before (or after) your amniocentesis. There are many conditions that cannot be detected by amniocentesis, and sometimes a genetic counselor (by looking at your family history) can help you explore concerns for which testing does not yet exist.

These counselors are also invaluable should your results be abnormal. Most of the conditions that can be diagnosed by amniocentesis can cause a spectrum of symptoms, and no two people with these conditions are the same. For example, while children with Down syndrome can be affected differently depending on the type they have, even children with the same type can have unique outcomes.

Tips

Here are some more tips to help you prepare for the procedure.

What to Wear

You will be undressed from the waist down during the procedure. It's a good idea to wear clothing that is loose fitting around your abdomen, as you may feel some abdominal cramping after the procedure.

Food and Drink

There are no dietary restrictions before an amniocentesis, but it's important to drink plenty of fluids. In some cases, a physician will encourage you to drink extra fluids and refrain from urinating so that you have a full bladder during the test, which can make the test easier to perform for the clinician. (A full bladder is more important if you are closer to 15 weeks gestation and less so if you are closer to 20 weeks.)

Cost and Health Insurance

Many insurance companies cover at least part of the cost of an amniocentesis. For those who do not have insurance, the average cost is between $1,500 to $2,500 but can range from less than $1,000 to over $7,000. If you will need to pay out of pocket for the procedure, some clinics offer reduced fees if you set up a payment plan ahead of time or can pay for the entire procedure at once.

What to Bring

Bring your insurance card to your appointment, as well as any forms you were advised to complete. If a physician other than your regular doctor will be performing the test, they will want to review your prenatal records before the test.

It's always a good idea to bring a book or something else to occupy you in case the doctor is running behind or your procedure is otherwise delayed. Even though you will probably be able to drive yourself, it's helpful (and can be comforting) to bring your partner or loved one to support you during the procedure.

Coping with Worry

While only a small percentage of women will get unwelcome news, some will—making waiting for your results stressful. Aim to take care of yourself physically (with rest, eating well, and light exercise) and emotionally (with self-care activities) while you await your doctor's call. Meditation, yoga, massage, spending time with friends, reading a book, and watching TV are all healthy, relaxing ways to cope.

Follow-Up

Follow-up after an amniocentesis will depend on your lab results. Most mothers will find out that their amniocentesis yielded normal results. A genetic counselor, your doctor, and/or other specialists can help you interpret the results of your amniocentesis if anything concerning was found during the test.

Clearly, finding out that something may be abnormal with your child is deeply upsetting. Seek the support you need to evaluate your options and to care for your emotional health during this trying time. Know that help is out there and that, once equipped with the relevant information from your doctor, you are the best person to decide how to proceed.

Occasionally, the results of amniocentesis are inconclusive. When enough fluid isn't obtained, an amniocentesis may need to be repeated.

A Word From Verywell

The decision to have an amniocentesis (and what to do if the results are abnormal) is often accompanied by significant anxiety. Serious concerns include the potential risks of the procedure as well as worry about conditions that may be found. Learning more about the procedure and potential findings may help to reduce some of this worry. Then, follow your heart and do what's right for you and your baby.