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Amniotic Fluid Analysis

Last updated July 25, 2019

Approved by: Krish Tangella MD, MBA, FCAP

Amniotic Fluid Analysis encompasses a range of tests that can be performed to evaluate the health of a fetus, through a procedure called amniocentesis.

What are the other Names for this Test? (Equivalent Terms)

  • Amniocentesis Fluid Test
  • Amniotic Fluid Test for Fetal Lung Maturity Tests

What is Amniotic Fluid Analysis Test? (Background Information)

  • During pregnancy, the amniotic fluid surrounds the fetus. It is a clear, pale yellow fluid, made in the membranous sac surrounding the fetus
  • The fluid aids in regulating the temperature of the fetus, as well as in protecting the fetus from injury. The total volume of amniotic fluid, at around 37 weeks of pregnancy, ranges from 500-1000 ml
  • The amniotic fluid contains various proteins, enzymes, hormones, antibodies, and also chemicals, produced by the fetus. Most importantly, it also contains cells shed by the fetus. These cells and chemicals contain genetic and other information, which may be used to diagnose chromosomal and genetic disorders
  • Amniotic Fluid Analysis encompasses a range of tests that can be performed to evaluate the health of a fetus, through a procedure called amniocentesis
  • Amniocentesis involves the removal of a small amount of fluid from the sac that surrounds a developing fetus, using a needle and syringe. Samples for the test may be obtained during the second trimester (between 15-20 weeks), or the third trimester (at around 32 weeks) of pregnancy
  • There are certain risks involved with the amniocentesis procedure and these may include:
    • The needle may puncture the fetus
    • It may cause a small amount of amniotic fluid leakage
    • There could be an infection
    • In rare cases, even a miscarriage could occur

What are the Clinical Indications for performing the Amniotic Fluid Analysis Test?

Amniotic Fluid Analysis may be used for chromosomal and genetic testing, and chemical analysis to assess certain conditions, in the 2nd and 3rd trimester.

During the 2nd trimester:

  • Family history of a chromosomal or metabolic disorder, or a genetic disease; or having a history of a previous child, with such an abnormality
  • Maternal age over 35 years, by pregnancy due date
  • Abnormal maternal screening tests, such as maternal serum alpha fetoprotein level (MSAFP), or abnormal findings detected on a fetal ultrasound
  • Risk of open neural tube defects, such as spina bifida
  • Risk of a sex-linked genetic disease

During the 3rd trimester:

  • Uterine infection
  • Fetal lung maturity, when there is a potential for premature birth
  • Rh incompatibility and related disorders
  • Presence of meconium (fetal bowel movement) that may have passed into the amniotic fluid, which may be an indication of a fetal distress

How is the Specimen Collected for Amniotic Fluid Analysis?

Sample required: A sample of amniotic fluid is obtained, using a procedure called amniocentesis.

Process: A small amount of amniotic fluid is withdrawn by inserting a needle through the walls of the abdomen and uterus, into the thin-walled sac of fluid that surrounds the developing fetus.

Preparation required:

  • Based on the gestational age of the fetus, either a full or empty bladder may be required to perform the Amniocentesis procedure
  • The area on the mother's abdomen is cleaned with an antiseptic medicine and a local anesthetic is applied, or injected into the skin
  • Before the procedure, the healthcare provider may use an ultrasound scan, to find the position of the fetus in the womb, in order to minimize the risk of injury to the fetus

What is the Significance of the Amniotic Fluid Analysis Result?

Genetic disease, chromosome abnormalities, and birth defects:

  • If a genetic disorder or chromosomal abnormality is detected, then the baby will most likely have the associated condition. It is important to note that such findings may not predict the severity of the condition
  • Not every chromosomal abnormality is detected through the test. Thus, the test does not guarantee the absence of an inherited disorder, in the fetus. Also, a genetic testing is usually performed for common mutation types

Fetal lung maturity:

  • Low levels of surfactants (soapy substance that lowers pressure on the lungs) are indicative that the fetus's lungs have not yet matured. Measures may be then taken to promote lung maturity, delay delivery, and prepare to treat the baby, as soon as it is born, if necessary
  • The healthcare provider monitors the level of surfactants. When their levels are high enough, the physicians may decide to deliver the baby safely, without an increased risk of complication

Additional and Relevant Useful Information:

  • Prior to the 2nd trimester, for chromosomal abnormalities and genetic disorder testing, an alternative test known as chorionic villus sampling (CVS) can be performed, instead of an amniocentesis
  • In the CVS procedure, a sample of placenta tissue at the site of implantation is collected. The test is performed between 10-12 weeks of pregnancy. The test carries similar risks, as an amniocentesis procedure and is not helpful in detecting neural tube defects
  • Due to the risks involved with both amniocentesis and chorionic villus sampling, these tests are not performed routinely, in all pregnancies

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

The following article link will help you understand the amniocentesis surgical procedure.


References and Information Sources used for the Article:

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: April 16, 2014
Last updated: July 25, 2019