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Amniocentesis

20 November 2024

The fetus grows in the uterus inside an amniotic sac that contains amniotic fluid. This fluid naturally discards fetal cells. An amniocentesis examines fetal chromosomes using the Genetic Chip Analysis, also known as chromosomal micro-array (CMA) and detects chromosomal disorders such as down syndrome. With the test, other genetic diseases may be diagnosed in the fetal DNA, but this is performed for a medical indication.

The test is largely performed between week 16 and until the end of week 22 of pregnancy. During the test, a small sample of amniotic fluid is extracted and sent to the laboratory. The laboratory will extract the genetic material (fetal DNA) from the sample and examine its chromosomal structure.

In certain cases, the test may also be performed at a later stage of pregnancy but only if there is a justifiable reason for performing it and only if a written recommendation is given following genetic counseling.

The ultrasound-guided test will be performed by a gynecologist, in a sterile manner, in order to choose the precise location to insert the needle that avoids approaching or potentially injuring the fetus.

Following the test, you should rest and avoid any exertion for 48 hours. You must also avoid sexual relations for 72 hours after the test.

Important to emphasize: the test is recommended for all women over the age of 32. The test is also recommended when there is a risk of a genetic disease in the fetus.

Potential risks and problems

  • Miscarriage: according to various studies, the risk of a miscarriage following an amniocentesis is between 1:400-1:1000 (0.1% - 0.25%).
  • Infection: an extremely rare complication since the process is performed under sterile conditions.
  • Insufficient or bloody sample: on rare occasions, the test fails to collect sufficient quantity of cells to extract fetal DNA required to perform the laboratory test, or alternatively - a bloody sample was collected, i.e. the fetal DNA mixed with the mother’s DNA.
  • Inconclusive test results: in other words, results indicate a chromosomal disorder but the impact on fetal health is not sufficiently clear.

Receiving results

Chromosomal test results of the fetus are generally received after 2–3 weeks. If other genetic tests are performed, the results will be received at a later date.

The fetus grows in the uterus inside an amniotic sac that contains amniotic fluid in which cells that contain fetal chromosomes are discharged. During an amniocentesis, a small sample of this fluid (the fluid renews itself within several hours) is extracted and sent to a genetic laboratory for diagnosis of chromosomal disorders, including down syndrome, and depending on a clinical need or recommendation, to detect the presence of genetic diseases in the fetus.

Since the amniocentesis is a form of direct testing of the fetus, it is considered a diagnostic test performed during pregnancy.

Objectives of the test

  • A test of the fetal chromosomes: normally, a fetus has 46 chromosomes that are divided into pairs: 22 pairs of autosomal chromosomes (chromosomes that are not sex chromosomes) and 2 sex chromosomes - XX for female and XY for male. Mutations in several chromosomes can cause various chromosomal disorders. The test is performed with a molecular method that examines fetal DNA using the Genetic Chip Analysis (also known as CMA). It can facilitate a diagnosis of Down Syndrome (characterized by an extra copy of chromosome 21) and can detect other mutations attributed to extra or missing chromosomal segments.
  • Diagnosis of a known hereditary disease in the family: if there is an increased risk of a certain disease, fetal cells will be tested to determine whether the fetus has the same disease. Technically, many and various genetic tests can be performed on fetal cells found in the amniotic fluid. For the most part, only relevant tests are performed based on the assessed risk of delivering a newborn with a certain disease. For example, amniotic fluid can be tested to determine whether a fetus is vulnerable to a degenerative muscular disease such as SMA, but this test is only performed when both parents are known carriers of this disease.

Date of the test

The test is mainly performed between week 16 and until the end of week 22 of pregnancy.

In certain cases, the test may also be performed at a later stage of pregnancy (mainly after week 32). In these circumstances, there must be a medical indication for the test and genetic counseling must be provided that recommends it.

Important to know

Important to know

Women who regularly take blood thinners, such as aspirin or Clexane, must inform the treating physician of the treatment and accordingly receive a recommendation to stop its use before the test (aspirin is generally stopped 5 days before the test and Clexane - 24 hours before the test).

Who should be tested

  • Age: the test is recommended for all women over the age of 32.
  • Abnormal findings in an ultrasound screening: in these cases, the recommendation is to continue investigation of the fetal condition by performing an amniocentesis.
  • Results of a biochemistry screening or nuchal translucency screening indicating increased risk of delivering a newborn with down syndrome: in these cases, the recommendation is to continue to investigate the fetal condition by performing the test.
  • Abnormal NIPT/ NIPS test: the results must be confirmed by an amniocentesis.
  • Increased risk of hereditary genetic disease: for example, when both parents are carriers of one of the diseases being tested for in the genetic screening, or if the parents already have a child with a known genetic disease (the recommendation is given during genetic counseling).

Important to emphasize: even if there is no special medical reason or abnormal findings in the fetus, the amniocentesis may be electively performed.

Stages of the test

An amniocentesis is performed in several stages to protect your health as well as the health of the fetus.

To make sure that the needle does not injure the fetus, during the first stage, the physician will perform an ultrasound to identify the fetal position in the amniotic sac and to make a decision on where to insert the needle.

Before the needle is inserted, the entire site will be disinfected to maintain maximum sterility.

Following disinfection, a long thin needle will be inserted through the abdominal wall into the amniotic sac to extract approximately 20-40 cc of fluid. The puncture will not cause bleeding and there is no need to dress the injection site. The place is usually disinfected after the puncture and sometimes a small pad is placed for a few minutes.

Important to know

Important to know

The puncture itself is very quick (almost like blood collection) and not painful but you may experience some discomfort during the test. Most places that perform the test allow you to bring a companion with you into the examination room.

Recommendations after the test

  • You should rest and avoid any exertion for 48 hours (you can receive approval for your place of work).
  • You must also avoid sexual relations for 72 hours after the test.

Potential risks and problems

  • Miscarriage: according to various studies, the risk of a miscarriage following an amniocentesis is between 1:400-1:1000 (0.1% - 0.25%). If you feel cramping (similar to contractions) in the lower abdomen, a feeling of wetness (possibly indicating your water breaking) or vaginal bleeding, you should seek immediate medical attention from the treating physician or Gynecology ER.
  • Infection: an extremely rare complication since the procedure is performed under sterile conditions. If your body temperature rises after the test, if you are experiencing chills or a general feeling of illness, you must seek immediate medical attention from the treating physician or go to the Gynecology ER.
  • Insufficient or bloody sample: on rare occasions, the test fails to collect sufficient quantity of cells to extract fetal DNA required to perform the laboratory test, or alternatively - a bloody sample was collected, i.e. the fetal DNA mixed with the mother’s DNA. In these circumstances, you will need to decide whether to undergo another test or rely on the results of the screening tests.
  • Inconclusive test results: in other words, results indicate a chromosomal disorder but the impact on fetal health is not sufficiently clear.

Receiving results

Chromosomal test results of the fetus are generally received after 2–3 weeks. If other genetic tests are performed, the results will be received at a later date. The laboratory team will update you according to the test.

  • Normal test result

    The result will be sent to you in accordance with standard procedures at the test site, e.g.: telephone call and signed document, sending the signed document by email, sending result by mail, uploading to the personal site of the HMO, etc.

  • Abnormal test result

    In this case, you will be invited for genetic counseling, where you will receive a thorough explanation about the test result and its implications for the fetus and fetal development. You will then need to make a decision on whether to continue the pregnancy or to apply to the Termination of Pregnancy Committee. If you choose to turn to the Termination of Pregnancy Committee, the staff at the institute will instruct you on the process.

Important to know

Important to know

If you choose to terminate the pregnancy, the process may involve premature delivery at a hospital - this depends, inter alia, on the age of the pregnancy and the medical recommendation.

Financing the test

There are several medical indications that entitle you to full public funding of the amniocentesis by the Ministry of Health or your HMO. In other cases, the test is funded by the patient or partially funded by the supplementary health services:

  • Every woman who is 32 years or older (on the date they became pregnant): the test is funded by the Ministry of Health.
  • Every woman under the age of 32 - the HMO will fund the test under the following circumstances:
    • Biochemistry screening (from the first or second trimester) indicates increased risk of Down Syndrome and genetic counseling recommended that the test be performed.
    • Results of the fetal nuchal translucency is over 3mm, i.e. - elevated nuchal translucency.
      NIPS/NIPT test - abnormal.
  • Woman under the age of 32 who has another medical reason, or who received a medical recommendation following genetic counseling: will be entitled to Ministry of Health funding once it received confirmation from the Genetic Department.

Important to know

Important to know

Eligibility for Ministry of Health funding of the test will only be provided if you have undergone the entire process without private funding (full or partial) and without funding of supplementary insurance from the HMO or private health insurance. Every woman can take the test privately.

Exercise of the eligibility

Additional amniocentesis tests

There are other tests that can be privately performed on amniotic fluid that was collected during the test, such as:

  • Tests that enable a rapid result to detect Down Syndrome (generally within 2-3 days), or a FISH test or a QF–PCR test.
  • Growth of amniotic fluid cells collected during the test by the end of the pregnancy, so that if a finding is discovered later in the pregnancy that requires the examination of the fetus, you will not have to undergo another puncture.
  • Exome test, a comprehensive genetic test of all functional units in genes, or genome test of the entire fetal genome. Today, these tests are not recommended during a pregnancy in which no significant abnormal findings were detected.

Information about these, and other tests, which are performed on amniotic fluid can be obtained during genetic counseling or at the site where you will undergo the amniocentesis. In any case, it is important to emphasize that these tests are private and not funded by the Ministry of Health or the HMO.

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