Amniocentesis: Procedure, Indications, Benefits, Risks, Accuracy

What is Amniocentesis?

Amniocentesis is a prenatal diagnostic procedure which can be used to determine the sex as well as abnormalities and infections of the fetus. In amniocentesis, amniotic fluid is extracted from the amniotic sac of females and studied. This amniotic fluid is the fluid that surrounds your baby before birth inside the amniotic sac and cushions your baby from shocks and injuries.

We all have heard the term “water breaking” that happens before birth of the baby which is actually leaking of pale yellow or clear fluid from the vagina that women experience at the onset of labor. This “water” is nothing but amniotic fluid only which leaks at the time of labor due to rupturing of membranes.

This amniotic fluid contains live fetal cells as well as alpha-fetoproteins (AFP). The fluid is extracted and studied to determine various problems in the fetus.

American obstetrician Fritz Friedrich Fuchs and Danish gastroenterologist Polv Riis were the first ones to perform the process of amniocentesis in 1956 even though they performed it without the use of ultrasound.

What is Amniocentesis?

Procedure of Amniocentesis

The procedure of amniocentesis follows the following steps:

  • This process is performed between 14th to 20th weeks of pregnancy.
  • Since a long needle is used to withdraw the fluid, the mother may feel pain during its insertion. To relieve this pain, a local anesthetic may be administered.
  • As soon as the anesthetic is in effect, the needle is inserted to withdraw the fluid.
  • This is done with the help of an ultrasound. An ultrasound wand is also placed on the abdomen to determine a place which is not very close to the baby and that is where the needle is inserted.
  • The needle is inserted in the abdominal wall of the mother, then the uterus wall and finally into the amniotic sac.
  • Approximately 20ml of amniotic fluid is extracted from the amniotic sac.
  • Replenishing of the lost amniotic fluid and resealing of the puncture made by the needle takes roughly up to 24 to 48 hours.
  • Amniotic fluid is taken and cells of the fetus are separated from it.
  • These cells are then cultured separately in a suitable culture medium in a lab.
  • These cells are then fixed and stained using a suitable dye.

The chromosomes of the cells are studied under a microscope to determine any genetic abnormality that may be present in the baby as well as to determine the sex of the fetus.

Indications & Benefits of Amniocentesis

Amniocentesis can be used for the diagnosis of a variety of genetic diseases and it can also be used as a treatment for excess amniotic fluid present in the sac. Some of the indications for the use of amniocentesis are given here:

Benefits of Amniocentesis in Diagnosing Genetic Abnormalities

Amniocentesis can be done to determine various genetic abnormalities. Some of them are:

Down Syndrome (Trisomy 21)

Down syndrome is a genetic disorder caused by an extra copy or third copy of the chromosome 21. People suffering from Down syndrome have some characteristic facial features and are mentally disable. This syndrome can be diagnosed before birth by the use of amniocentesis.

Trisomy 18

Trisomy 18 is also known as Edwards syndrome. This is caused by an extra copy of chromosome 18. Babies suffering from this syndrome are born small with heart defects and intellectual disabilities. This can also be diagnosed early by using amniocentesis.

Trisomy 13

Patau syndrome is another name of trisomy 13 in which there is an extra copy of the chromosome 13. This causes people suffering from Patau syndrome to have multiple organ defects as well as abnormal growth. Amniocentesis can help in diagnosing this genetic disorder before birth.

Fragile X Syndrome

Fragile X syndrome is another one of the genetic disorders that can be detected with the help of amniocentesis. In this syndrome, children suffer from mild to moderate intellectual disability. Autism and hypersensitivity are also some of the symptoms.

Neural Tube Defects

Neural tube defects are some defects that arise when the brain and spinal cord openings which are formed during the development of the baby; do not close properly. Anencephaly and spina bifida are two of such neural tube defects that can be detected by studying the levels of alpha-fetoproteins through the amniocentesis process.

Inherited Metabolic Disorders

Inherited metabolic disorders also called as inborn errors of metabolism; are congenital disorders of metabolism that are inherited from one generation to another and are caused by the presence of defects in the single genes. They can also be detected with the help of amniocentesis.

Amniocentesis for Lung Maturity Testing

Amniocentesis can be beneficial in the testing of lung maturity in the fetus. For this purpose, amniotic fluid is extracted and then tested using a variety of tests to determine whether the lungs are mature enough for birth. If they are not mature enough, the baby runs the risk of suffering from infant respiratory distress syndrome.

Diagnosing Fetal Infection

One of the benefits of Amniocentesis is that it can be done to determine fetal infections. For this purpose, amniotic fluid is stained with Gram stain to show the presence of bacteria. It can also be tested for the number of white blood cells and if there is any abnormality in their count, it can indicate infection in the fetus. Amniocentesis can also detect a decreased glucose level.

Detect Rh-Incompatibility

If the baby is suffering from Rh-incompatibility sensitization, amniocentesis can be used to check on the progress and well-being of the developing fetus even though doctors nowadays prefer to use Doppler ultrasound instead of amniocentesis. Rh-incompatibility is a condition that occurs when the Rh-factor of the mother differs from that of the baby. For example if the mother’s blood is negative and the fetus is positive or vice versa. This condition may lead to some complications and may even cause miscarriage of the pregnancy.

Decompression of Polyhydramnios

Amniocentesis is also beneficial in draining excess amniotic fluid from the uterus of the mother to cure a condition called polyhydramnios in which mothers accumulate excess amount of amniotic fluid.

Risks of Amniocentesis Procedure

There are some possible risks of amniocentesis procedure. These include:

Miscarriage of Pregnancy

A recent study has shown the risk of miscarriage from amniocentesis to be around 0.06% which means 1 in 1600 cases. This is much less than the number indicated by earlier studies because it excluded the cases in which parents opted for abortion due to genetic abnormalities. It only took the number where miscarriage occurred due to complications from amniocentesis procedure, even though it is very difficult to estimate the number of miscarriages that occur due to amniocentesis as a certain number of miscarriages occur in second trimester anyway from complications that have nothing to do with amniocentesis.

Fetal Injury

There is also a risk of fetal injury which is greatly increased if amniocentesis is performed before 14th week of the pregnancy. If amniocentesis is performed in the 11th to 13th week, it is termed as “early amniocentesis” and there is a greater risk of fetal injury in that.

Transmission of Diseases

Amniocentesis may transmit such diseases as hepatitis C and HIV/AIDS to the baby, if the mother is suffering from them. Amniocentesis may also cause uterine infection in the mother even though this happens very rarely.

Amniotic Fluid Leak

Amniocentesis process may result in amniotic fluid leak. This is a rare occurrence and usually only a small amount of the fluid leaks through the vagina which stops in one week’s time. In most cases, baby suffers no ill effects from this.


If the mother has Rh-positive blood and the baby’s blood is Rh-negative, the baby’s blood may enter the bloodstream of the mother due to amniocentesis process. As a result, the mother develops antibodies against Rh-positive blood which can cross the placenta and can cause baby’s blood cells to get destroyed.

Other Risks of Amniocentesis

Apart from the above mentioned risks, there is also the risk of preterm labor and delivery. Amniocentesis may cause an early birth. It can also lead to postural deformities, respiratory distress in which the baby experiences a difficulty in breathing and chorioamnionitis which is an inflammation of the fetal membranes.

The amniocentesis process, besides having medical risks, also has some social complications. Since the process can be used to get rid of “disable babies”, there is a risk that the process may be abused to get rid of people with perceived disabilities. There is also a risk of increased discrimination against people with disabilities. So there is also pressure on parents to make a rational and ethically correct decision regarding the life and well-being of their baby which can be quite distressing and emotionally taxing.

How to Reduce the Risks of Amniocentesis?

There are many ways in which you can reduce some of the risks associated with amniocentesis. Some of these things are mentioned here:

  • Choose a doctor who has a lot of experience in such cases.
  • Choose a center which performs lots of amniocentesis procedure and whose rate of miscarriage after the procedure is very low.
  • Make sure they have trained personnel such as the person who will perform ultrasound during the procedure. Make sure he or she is an experienced and registered diagnostic medical sonographers.

If you take the above mentioned precautions, it will increase your chances of having an accurate and relatively safer amniocentesis procedure. If the personnel are experienced, it will also reduce your chances of going through the procedure again due to the removal of inadequate amount of amniotic fluid and it will also keep your baby from needle injuries etc.

What to Do After Amniocentesis Procedure?

After the procedure of amniocentesis is done, you should follow the below mentioned guidelines for aftercare:

  • Make sure that you rest comfortably for the rest of the day after the amniocentesis procedure is done.
  • Avoid exercise and strenuous activities of any kind for a couple of days after having amniocentesis done.
  • Do not lift anything heavier than 20 pounds after getting amniocentesis performed.
  • Refrain from any sexual activities for a day or two of having amniocentesis.
  • Contact your doctor immediately if you experience any kind of problem after amniocentesis process such as vaginal bleeding or intense pain etc.

Accuracy of Amniocentesis Procedure

Amniocentesis procedure has a high accuracy rate of about 99.40%. It may fail sometimes, if sufficient amount of amniotic fluid could not be collected. Sometimes even though adequate amount of amniotic fluid is collected, the cells fail to grow in the culture medium which can also cause the failure of the amniocentesis procedure.

Also Read:

Pramod Kerkar, M.D., FFARCSI, DA
Pramod Kerkar, M.D., FFARCSI, DA
Written, Edited or Reviewed By: Pramod Kerkar, M.D., FFARCSI, DA Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:January 23, 2018

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