Amniocentesis: when is it done and what does it test for?

Mums-to-be have quite a busy agenda with all the antenatal appointments during which the health of both mother and baby is checked. In addition to the routine antenatal checks and tests, there are a few screening and diagnostic tests that are only done if there are signs of complications or if it is suspected that the baby might have a condition. One of these additional tests is amniocentesis.

What is amniocentesis? When is it done? What does a standard amniocentesis procedure look like? What are the risks? And what does amniocentesis test for?

What is amniocentesis and what is it used for?

What is the process of amniocentesis?

Amniocentesis: risks and benefits compared

Amniocentesis yes or no: aspects to consider

Preparing for amniocentesis: talking to other mums

Frequently asked questions about amniocentesis

Amniocentesis: key takeaways

What is amniocentesis and what is it used for?

Amniocentesis is a medical procedure which is used during pregnancy to check if the baby has certain genetic conditions. It is an amniotic fluid test that can be performed from the 16th week of pregnancy.

It involves puncturing the amniotic sac with a needle to remove a small sample of amniotic fluid which is then analysed in a laboratory. The aim is to check for signs of a chromosomal or genetic condition in the baby. This includes hereditary diseases as well as changes in the number of chromosomes, such as trisomy 21 (also known as Down's syndrome).

In contrast to other antenatal screening tests, the amniotic fluid test is an invasive procedure. This means that the procedure invades the mother’s body, which is associated with an (albeit low) risk.

Therefore, the procedure is only performed if the treating health professional or doctor suspects that the baby might have a condition. For instance, one of the prenatal ultrasound scans might have shown certain abnormalities.

What is the process of amniocentesis?

Put simply, amniocentesis describes the process of removing amniotic fluid for analysis. This involves puncturing the amniotic sac with a needle to get a sample.

During the procedure, the health professional inserts a needle through the mother’s abdominal wall until it reaches the amniotic sac. In order to prevent any harm to the baby, the baby’s position is monitored via ultrasound scan.

The procedure itself typically doesn’t take longer than one to two minutes. However, it is preceded by a detailed medical consultation. During the consultation, the health professional or doctor explains the pros and cons of the procedure and answers any questions the mother might have. Finally, the mother needs to give her written consent for having amniocentesis.

In a next step, the amniotic fluid sample is analysed in a laboratory. The first results should be available within a couple of days. However, it can take up to two to three weeks before the final results are available because the cells might first have to be multiplied for analysis.

The amniotic fluid sample can be analysed in two different ways. The main purpose of the analysis is to check the structure and number of chromosomes in the baby’s cells. Additionally, the amniotic fluid can be tested to see if there are any infections.

Amniocentesis: risks and benefits compared

Since an amniotic fluid test is an invasive procedure, there is a low risk of miscarriage. Less than one percent of all women who have amniocentesis lose the pregnancy after the procedure. In even fewer cases, the procedure leads to infections, uterus bleeding or amniotic fluid loss.

In theory, there is a chance that the baby might get injured through the needle. However, the risk of this happening is very small because the baby’s position is monitored through ultrasound scan before and all the way through the procedure.

Having amniocentesis can, however, pay off despite these risks. That’s because the test delivers definitive results and provides clarity on any suspected conditions in the baby. Further benefits of amniocentesis include that it:

delivers very reliable test results
provides certainty about the baby's state of health
can be used for several tests with just one sample (infections, hereditary diseases and number and structure of chromosomes)

However, parents who are expecting a baby should bear in mind that amniocentesis results can also be distressing. For example, the test may reveal that the baby has an untreatable condition such as trisomy 21. Parents therefore shouldn’t hesitate to get professional support before the procedure.

Amniocentesis yes or no: aspects to consider

Due to the fact that the procedure involves a small risk for mother and baby, amniocentesis is not performed without reasons. It is only offered in cases where the doctor or health professional who is in charge of the mother’s antenatal appointments suspects a chromosomal disorder or another illness in the baby or where there are other medical reasons for having an amniotic fluid test.

Possible reasons for having amniocentesis include:

advanced maternal age (typically 35 years or older)
abnormalities detected during an ultrasound scan
suspicious results from another antenatal screening test
family history of hereditary diseases
genetic conditions in older siblings

In almost all cases, an amniotic fluid test delivers definitive results and can clearly confirm or refute any previously made diagnosis. However, before deciding on whether or not to undergo the procedure, expectant parents should consider the possible consequences of the final diagnosis.

Preparing for amniocentesis: talking to other mums

Amniocentesis is not without risks. Despite an in-depth medical consultation, mums-to-be are often unsure about whether to have the procedure or not and what the results could mean for them and their baby. Talking to other mothers who have been in the same situation can help.

Pregnancy groups and online communities are great for connecting with other mums-to-be and sharing experiences. Hearing about the experience other expectant mothers have had with amniocentesis can take away the fear of the procedure and help make the right decision.

Frequently asked questions about amniocentesis

Just like chorionic villus sampling, amniocentesis is a prenatal diagnostic test that is not part of the usual antenatal tests and screenings. Since it is not part of the standard repertoire of tests offered to all pregnant women, mums-to-be often have many questions. Read on as we answer the most frequently asked questions about amniocentesis.

What is amniocentesis?

Amniocentesis is an invasive medical procedure that is performed during pregnancy to check if the baby has a genetic condition or certain hereditary diseases.

When is amniocentesis offered?

Since the procedure carries a small risk for the baby, it is only performed if the treating doctor or health professional suspects a condition. This could be because a previous ultrasound scan has shown abnormalities or because other antenatal screening tests have delivered positive results. Another reason why an amniotic fluid test might be offered is when there is a family history of certain genetic conditions.

What does amniocentesis test for?

Amniocentesis can test for certain disorders and conditions. These include:

infections that have been passed on to the baby (e. g. toxoplasmosis)
hereditary metabolic and muscle diseases
development disorders such as neural tube defect
chromosomal disorders (e. g. trisomies 13, 18 and 21)

What happens during amniocentesis?

After an in-depth medical consultation regarding the benefits and risks of amniocentesis, the health professional inserts a needle through the abdominal wall and into the amniotic sac to remove a sample of amniotic fluid. The sample is then sent to a laboratory for testing.

How painful is amniocentesis?

Inserting the needle through the abdominal wall can be slightly painful. Most women who had amniocentesis compare the pain to having a blood sample taken. That’s why the procedure is usually performed without use of anaesthetics. Some mums-to-be experience cramps in the abdomen for a few hours (or even a few days) after the procedure.

How accurate are amniotic fluid tests?

Amniocentesis gives a definitive result in almost all cases. In contrast to antenatal screening tests that only indicate that the baby may have a condition, a diagnostic test like amniocentesis provides certainty on whether the baby will be born with a condition or not.

Amniocentesis: key takeaways

Amniocentesis is a diagnostic test performed during pregnancy which involves a detailed analysis of the baby’s cells taken from a sample of amniotic fluid.
The aim is to provide clarity on whether or not the baby will be born with a genetic or chromosomal condition.
An amniotic fluid test is typically offered if there is an increased risk that the baby might be born with a condition.
Factors that increase the risk of having a baby with a condition include advanced maternal age, family history of hereditary diseases or abnormalities discovered during a previous ultrasound scan.
The procedure can be performed from the 16th week of pregnancy onwards.
Amniocentesis delivers definitive results, but it also involves a small risk for mother and baby. Roughly one percent of the women who have amniocentesis lose their pregnancy afterwards.