All about amniocentesis

Amniocentesis (also called as amniotic fluid test, amnio for short, and abbreviated as AFT) is an express permission prenatal test which involves the extraction of amniotic fluid to diagnose various birth defects and genomic conditions.


The extracted amniotic fluid serves as a prenatal diagnostic tool to detect any concerns on the following substances:

  • Fetal cells
  • Amniotic chemicals and microorganisms

All of which provides all the needed information about the growing fetus such as hereditary characteristics, present health condition, and level of maturation (particularly the lungs).

When is amniocentesis test necessary to take?

Amniocentesis test is generally performed between 14 – 20 weeks of gestation; some hospitals offer it for as early as 11 – 13 weeks; while some take it for as late as 23 – 24 weeks. In general, here are the following reasons when this test is necessary to take:

  • For pregnant women with age 35 and above – the risks of carrying a baby with birth defects and chromosomal abnormalities increases as she gets older
  • Family record of certain genetic disorders – if the expectant mother, her spouse, or a member of either of their families suffer from genetic disorders
  • A history of a pregnancy birth defects
  • The couple had a previous child with chromosomal disorders
  • Abnormal results from prenatal screening tests such as first – trimester blood sample, non – invasive prenatal screening (abbreviated as NIPT, commonly called as ultrasound), alpha – fetoprotein levels, amniotic fluid evaluation, and multiple (triple or quad) marker screening
  • For expectant mothers whose membranes have ruptured earlier
  • Checks the current level of anemia for fetuses with Rh disease
  • Helps physician decide if the fetus needs a blood transfusion
  • If a pregnant woman is required to induce labor
  • Expectant mother carries an x – linked recessive inheritance, which will highly likely be passed down if she is bearing a son
  • Parents carry an autosomal recessive inherited disease which will likely be passed down on the fetus

 Performing an amniotic fluid test

Did you know that medical facilities and maternity clinics performed an amniotic fluid test for about 200,000 times per year? With that being said, enlisted below are the following step – by – step procedures of taking a diagnostic amniocentesis:

Pregnancy week by week
  1. First and foremost, the perinatologist (the maternal and fetal specialist who performs the amniotic fluid test) will ask the expectant mom to lie on her back. A drape will be placed over her and leaving just the bump exposed.
  2. Some perinatologist inject a local anesthesia on the area to be punctured. However, since being anesthetized is as painful as the amniocentesis, most perinatologists opt not to use it. Initial set – up usually lasts for about 30 minutes.
  3. Before proceeding to the amniotic fluid test, the perinatologist will use an ultrasound to detect baby’s current size – to confirm that the pregnancy has reached the 14th week), to locate the amniotic sac’s position together with the placenta, and the amniotic fluid volume.
  4. Then an anti – bacterial iodine solution is rubbed onto the abdomen. This liquid solution is applied to clean the abdomen and kill germs on the skin’s surface.
  5. Next is the ultrasound transducer to capture the image of the fetal position. A transducer also serves as a simultaneous guide to determining a safe area for the needle to puncture the amniotic sac.
  6. Once the safe area is determined, the perinatologist punctures a long and narrow needle through the abdominal and uterine wall into the amniotic sac.
  7. The injected needle is navigated carefully via the images shown on the ultrasound monitor. The painful injection usually takes for about 2 minutes.
  8. The fluid is then extracted and collected safely, preventing the fetus together with its placenta from being accidentally pricked in the course of the procedure.The needle collects at least an ounce (1 – 2 tablespoons) of amniotic fluid – also called as a pregnant woman’s water, it is the fluid which surrounds the fetus and contains shed cells.
  9. Once the desired amniotic fluid is extracted through the needle (collecting the fluid lasts for only 5 minutes), the perinatologist carefully extracts the sample.
  10. The collection of amniotic fluid is sent to the medical laboratory for analysis. In the laboratory the fetal cells are separated from the fluid, and the genetic materials are examined for any defects and postnatal disorders. Amniotic fluid sampling results are made available after 2 weeks.
  11. The laboratory may also trace if there are any proteins (specifically alpha fetoprotein, abbreviated as AFP) in the amniotic fluid. The levels of AFP can determine if the fetus has neural tube deficiencies. If the AFP levels are high, the unborn baby suffers from NTD. AFP analyzation results are available within a few days to a couple of weeks, depending on the intricacy of the exam.
  12. Parents who are carriers of genetic disorders such as Tay –Sachs disease and cystic fibrosis will require a more intricate examination of the amniotic fluid collection. If the fetus is being examined for genetic disorders, the cells are cultured for at least 10 – 12 days so that there are enough samples for further testing.
  13. After the procedure, the expectant mom will undergo Rh factor testing. If the result is Rh negative, the perinatologist will provide a Rh – immune globulin injection (RhoGAM for short) to prevent future Rh complications.
  14. The amniocentesis procedure usually lasts for about 45 minutes.
  15. An expectant mom who underwent amniocentesis is advised to take a bed rest for a day or two.

Perinatologists and medical practitioners in general highly recommend taking the amniotic fluid test during the 2nd trimester (between 15 – 20 weeks). While amniotic fluid test during the 3rd (and last) trimester can trace any infections in the womb.

An amniocentesis being performed before the 15th week of gestation is highly discouraged since imposes to a higher risk of miscarriage and other pregnancy complications.

Amniocentesis test results

Amniocentesis test results are made available after 2 weeks. However, even though the chances of identification are highly likely, AFT does not measure the seriousness of the detected birth defects. Furthermore, below are the percentage rates of AMT results:

  • Down syndrome – 99%
  • Other chromosomal deformities – 90%
  • Spina bifida – 90%

For faster AFT results (regularly within the day or two), some laboratories use the fluorescent in situ hybridization (abbreviated as FISH) – a method which speeds up the counting of the chromosomes within the fetal cells. Amniocentesis combined with a FISH method and results are 98% accurate.

If the amniotic test results indicated a complication, the perinatologist and a genetic specialist will provide expectant parents some counselling. This type of counselling will discuss matters and options about the following enlisted below:

  • Possible distressing scenarios in the latter months of gestation
  • How to deal with a child with birth defects and genetic abnormalities (if not prevented via the amniocentesis)
  • Be well – provided with knowledge and information to prepare expectant parents on taking care of a baby with birth defects and abnormalities
  • Helps expectant parents be emotionally prepared with taking care a defected child
  • How such birth defects and hereditary abnormalities have surfaced
  • Possible medical treatment options if ever the baby is born with defects
  • Possible surgeries the baby will undergo if ever he is born with deformities
  • Possible surgeries before childbirth

What is an amniotic fluid test for?

Occasionally, an amnio test is offered during the latter weeks of gestation to see if there are any hereditary or genomic concerns. This test is considered as the most precise test available to check, detect, and determine the following fetal factors enlisted below:

  • Detects any uterine infections
  • Detects any fetal abnormalities
  • Detects neural tube deficiencies such as spina bifida
  • Specifies any genetic disorders such as sickle cell anemia
  • Examines the extracted amniotic fluid for chromosomal deformities
  • Traces any fetal infections such as erythema infectiosum (commonly called as the 5th disease)
  • Checks if there are any chromosomal abnormalities
  • Checks the level of maturity of the fetal lungs to function on their own. In this case, amnio is done right before labor and delivery
  • Sex determination – reveals the unborn baby’s gender
  • Accesses the DNA (deoxyribonucleic acid) for paternity testing prior to childbirth. The potential father’s DNA is compared to the fetus’s DNA that is collected via the amnio. The results are 99% accurate of determining and tracing the biological relationship between the man and the baby. This ensures the child’s well – being and protect his future


The aftermath of amniocentesis

The mere thought of having a long and thin needle will puncture deep into one’s body and near the unborn baby is frightening. But with the simultaneous guide of sonography, the chances of pricking the fetus is highly unlikely to happen.

Some women who already underwent the needle stated that the amnio process does not hurt that much since the needle is too thin to cause much pain.

Contrary to that, others feel cramping as the needle perforates the abdomen and pressure as the perinatologist draws out the amniotic fluid. As a matter of fact, studies show that 1 – 2 out of 100 pregnancies experience cramps, vaginal bleeding, and amniotic fluid leakage after the test.

In the course of the amniotic fluid test, below are the following sensations that pregnant women who are required to take the test must expect:

  • Severe abdominal cramping as the needle burrows deep
  • Drawing sensation as the needle with the collected fluid sample is being pulled out

Side effects and risks of amniocentesis

Even though an amniocentesis is considered to be a harmless medical procedure, it is also widely recognized as an intrusive analytic examination that imposes probable side effects and risks such as the following enlisted below:

  • Miscarriage – this is considered as the primary risk following the AFT. As a matter of fact, studies show that less than 1 out of 200 pregnancies have miscarried after taking amniocentesis
  • Vaginal bleeding and/or spotting (rarely occurs)
  • Amniotic fluid seepage (rarely occurs)
  • Slight irritation around the perforated area
  • Mild abdominal cramping
  • Pricking sensations in the uterus
  • Back pain
  • Pain and discomfort around the punctured area

Chances are, the fluid seepage and spotting side effect will stop after a few days.

If these risks and side effects worsen, immediate medical attention is required.