What is an Amniocentesis? Reasons for & Risks

Amniocentesis is a prenatal diagnostic test in which a sample of the amniotic fluid is taken. The fetus is constantly shedding cells into this fluid, hence it used to diagnose a lot of conditions such as Down syndrome and determine if the fetus has an infection1. It is also used for genetic testing to determine if the fetus has a genetic condition that runs in the family or simply to determine paternity. If you are unsure if this procedure is recommended for you, contact your doctor or schedule an appointment to speak to one of our obstetricians in Manhattan today. The levels of the amniotic fluid is very important and is watched closely throughout pregnancy. As such, only a very small amount of this fluid is taken during this procedure (no more than an ounce). Below is a list of functions the amniotic fluid performs:

  • Protects the fetus by absorbing or reducing the shock caused by the physical trauma (hits or blows to the abdomen). This reduces any possible injury to the fetus2.
  • Protects the fetus from infection/reduces the chances of infections.
  • It helps to regulate the temperature of the fetus.
  • Allows the fetus to develop and move properly. The amount of amniotic fluid available is very important and an incredible low amount would cause your doctor to advise an early delivery in order to protect the baby as fetal development may become regarded.

There are also periods during pregnancy when this procedure is considered risky. Any test done before the 15th week is considered riskier and carries a higher possibility of miscarriage, which is usually around 0.1-0.3% after this period1. This procedure can also be used as a treatment for certain conditions.

Reasons to have an Amniocentesis

There are a number of reasons this procedure is carried out. In most cases it used to diagnose a certain condition and in other cases it is used as a treatment regimen. Below is a list of some of the possible reasons your doctor may recommend an amniocentesis.

Mother’s age

Babies born to mothers who turn 35 during pregnancy or are above 35 have a higher chance of developing chromosomal defects or conditions such as Down syndrome.

Genetic/chromosomal test

Here a sample is taken to rule out genetic conditions that might run in the family of the fetus’s mother or father. This test is also recommended if an older child was born with a birth defect.

Neutral tube defect (spinal bifida)

This is a condition that affects the brain and the spinal cord of the fetus, hence this procedure is highly recommended especially if a child in the family was born with this condition3.

Paternity test

Since the amniotic fluid contains cells shed from the fetus, this can be used to determine paternity. The DNA test will be carried out with these cells to determine if there is a match between the fetus and the potential father1.

Fetal Lung test

This procedure is recommended if an early birth is required. Here a sample is taken to determine whether the baby’s lungs are mature enough for birth.

Diagnosis of Infection

A sample is taken to determine if there is an infection or some other illness affecting the fetus. For those with Rh sensitivity, it is used to determine the severity of the fetus’s anemia. This is a condition where the mother’s immune system attacks the fetus’s blood cells.

Treatment of polyhydramnios

In this condition, there is too much amniotic fluid and this can lead to premature birth. Premature birth is any birth that occurs before the 37th week of pregnancy3.

What are the risks associated with an Amniocentesis?

Though low, there are still risks associated with this procedure. Below is a list of some complications associated with the procedure

  • In rare cases, women have developed a uterine infection after this procedure.
  • There is a small risk of miscarrying (0.1-0.3%), especially if your procedure is performed before the 15th week.   
  • Though uncommon, some women leak amniotic fluid after the procedure; this leak is usually only a few drops or a small amount and stops within a week. After which, pregnancy proceeds normally. However, if you are losing an excessive amount of fluid or it has not stopped after a week, immediately contact your health provider.
  • The baby may move his or her hands/legs during the procedure and this may lead to needle injury. However, the injuries resulting from this accident are rarely ever serious.
  • Transmission of infections such as HIV/AIDS from mother to child. Remember, during pregnancy, the baby remains in a sac that contains the amniotic fluid. This barrier also serves to protect the baby from infections in the mother’s bloodstream. Puncturing a hole into this sac would allow for the mother’s cells to enter and infect the child. Moreover, the mother’s body usually replaces the sample extracted with its own fluid.

It is always important for couples to weigh the risks and mother health before deciding to proceed with this procedure.

When is it safe to have an Amniocentesis?

As this is a medical procedure, there will always be some risk associated with it. However, there are certain situations and periods during pregnancy that pose a greater risk to the fetus. For instance, the position of the baby’s placenta, and mother’s anatomy may make this procedure riskier in some cases. Usually the risk of complication is very low and the risk of miscarriage for second-trimester procedures ranges anywhere from 0.1-0.3% depending on the location where the procedure is performed. That is, if this procedure is performed at a facility that does this on a regular basis, you chances of complication goes down to 0.1%. The stage of pregnancy is also very important as those performed before the 15th week come with a greater chance of complications and may lead to a miscarriage.

Deciding which procedures and prenatal tests to perform can be scary, however, the more information you have, the more confidence you will feel about whatever decisions you make. Contact us today to consult with one of OBGYN in NYC.


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1 Comment

  1. 67th Street OB/Gyn

    Hello Cary,
    Amniocentesis is the sampling of amniotic fluid using a hollow needle inserted into the uterus, to screen for developmental abnormalities in a fetus. We would love to help you. Please contact us if you have any questions.


  1. Cary - What is an Amniocentesis?