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Amniocentesis

What is amniocentesis?

Amniocentesis (also referred to as amnio, amniotic fluid test or AFT) is a prenatal testing procedure with significant accuracy. It involves collecting an amniotic fluid sample from the uterus and testing it in the laboratory for certain fetal abnormalities and genetic conditions. [1]

Who should have amniocentesis?

  • Women over 35 years old (babies born to older women are more at risk of developing genetic conditions like Down syndrome) [2]
  • Women with a history of a neural tube defect (a condition affecting the brain and spinal cord) or any chromosomal condition in a previous pregnancy [13]
  • Women with positive results from prenatal screening tests such as a blood test or noninvasive prenatal testing [3]
  • Women who have a family history of any genetic condition like cystic fibrosis, sickle cell disease and Down syndrome [4]

Why is amniocentesis performed?

  • For detecting hereditary conditions like spina bifida [5], Down syndrome and fragile X syndrome
  • For assessing the lung maturity of the baby if an early delivery is required due to some pregnancy complication
  • For detecting intrauterine infections
  • For finding out whether the baby has any life threatening conditions like Edward’s syndrome (Trisomy 18), Patau syndrome (Trisomy 13) and Tay-Sachs disease
  • For assessing the health of the baby in case the mother has a blood sensitization, like Rh sensitization (a serious condition that occurs when the mother has a different blood type than the baby). But at present, obstetricians often use a Doppler ultrasound instead of AFT for detecting such conditions.
  • For determining the gender of the baby [6]
  • For decreasing the amniotic fluid volume within the uterus (rarely in cases of polyhydramnios)

When is amniocentesis performed?

AFT is usually performed during the second trimester, particularly between the 15th and 20th weeks of pregnancy [7]. It may also be performed during the later stages of pregnancy (third trimester), especially before a pre-term delivery or a c-section birth.

Guidelines to prepare for amniocentesis

  • Drinking lots of water may be recommended prior to the ultrasound as a full bladder helps to produce better results
  • One may be advised not use Aspirin pills for five days before the amnio procedure [8]
  • One may be asked to avoid heparin and Lovanox for 24 hours before the procedure

What is the procedure of amniocentesis?

The step by step procedure includes performing an ultrasound to ascertain the positions of the baby, the placenta and the amniotic fluid pockets, then disinfecting the mother’s belly area with an antibacterial solution to prevent infecting the fluid while collecting the sample [7]. Next, the diagnostician collects around one ounce of amniotic fluid using a thin needle while monitoring the path of the needle on ultrasound. The ultrasound also helps to make sure that the baby’s heartbeat is normal after collecting the fluid sample. It is then sent to a clinical laboratory for karyotyping [18] – a process used for examining the chromosomes in the cells within the sample.

Amniocentesis Tests

Amniocentesis Tests

Does amniocentesis hurt?

It is not a painful process as most women feel only a sharp pinch, along with a lot pressure, when the needle goes through the uterus. Some women can barely feel it when the needle is run through the abdominal skin, but may feel a sharp pain when the needle goes through the uterus (it does not last for more than a few seconds).

Does amniocentesis need any aftercare?

  • Doctors recommend 24-hour bed rest following the test
  • Following a healthy diet containing fresh fruits, vegetables and dairy products
  • Drinking ample amounts of fluid
  • Practicing relaxations techniques as the stress and anxiety associated with the test may be harmful for the baby [9]

How long does it take to get the amniocentesis results?

Depending on the purpose of the test, the results are available:

  • Within 10 days (when checking fetal abnormalities like neural tube defects and protein levels in the fluid)
  • Up to 2 weeks (when checking for any genetic conditions in the baby)

Having a FISH (fluorescent in situ hybridization) test along with an amnio helps to get the results within a couple of days instead of weeks. It has a significant accuracy rate in predicting chromosomal abnormalities in the baby. [14]

Are there any side effects of amniocentesis in the mother?

It is a fairly safe screening procedure that often does not cause any side effects; however, some women may experience:

  • Mild to moderate cramping that continues for a few hours after the fluid sample is collected
  • Soreness and irritation around the spot where the needle was inserted (usually lasts for a couple of days) [10]
  • Continuous vaginal wetness due to leakage of amniotic fluid
  • Moderate to severe headache (rare)

What are the risks of amniocentesis for the baby?

  • Amniotic Fluid Leakage: Occurs after the test, often stopping on its own without causing any serious complications. However, in some cases, chronic fluid leakage may lead to orthopedic complications for the baby. [11]
  • Needle Injury: The baby may get injured by the needle if it moves a leg or an arm into its path. However, serious injuries of this kind are rare.
  • Rh sensitization: In some rare instances, the test leads the blood cells of the baby to enter the bloodstream of the mother [11]. This may cause various complications if the mother has Rh negative blood (in such cases, the mother is given Rh immunoglobulin following the test to prevent her body from generating antibodies against the baby’s blood cells).
  • Uterine Infection (rare)
  • Infection transmission: If the mother is affected by an infectious disease, like toxoplasmosis, hepatitis C or HIV, the infection may be transferred to the baby during the examination.
  • Scarring: Sometimes, the baby may be born with a small depressed scar resulting from an amnio test performed during mid-trimester. [12]

What are the odds of a miscarriage following an amniocentesis?

The risk of miscarriage associated with the test ranges from 1 in 300 to 1 in 500 [11]. According to researchers, having amniocentesis before the 15th week of pregnancy increases the danger of a miscarriage. The chances of miscarriage are somewhat higher in women carrying twins or triplets.

What are the limitations of amniocentesis?

  • An AFT can rule out only certain chromosomal and genetic disorders in the baby. It cannot detect conditions like autism, non-specific mental retardation, cleft lip and various heart defects [6]. So, having a negative test result does not guarantee that one will have a normal baby.
  • Although amnio produces accurate results, it is sometimes difficult to interpret them. Such cases may call for additional chromosome testing. [17]

Amniocentesis Vs Chorionic Villus Sampling

Chorionic villus sampling (CVS) is another prenatal screening test that helps with the diagnosis of chromosomal abnormalities in the fetus. Although, the basic purpose of both amnio and chronic villus sampling is to detect chromosomal or genetic abnormalities in the baby, their procedures are completely different. CVS involves collecting cell sample from the tiny finger-like projections called chorionic villi, located on the placenta [15]. The sample is then sent to a lab for genetic analysis.

One of the main advantages of amnio over CVS is that the former can detect neural tube defects (spina bifida) as well as chromosomal defects in the baby [15] while the latter cannot. On the other hand, CVS has the advantage over amnio as it can be performed during the first trimester (typically between the 11th and 12th week), which enables parents to know whether their baby has any serious birth defects at an earlier stage.

Are there any alternatives to amniocentesis?

There is a new non-invasive fetal DNA test that can be used instead of amnio [16]. This cell-free blood test produces accurate results while there is no risk of miscarriage. In this test, a blood sample is collected from the mother to examine the DNA of the baby for any abnormalities.

How much does an amniocentesis test cost?

Its cost may vary from one country to another, ranging from $1,000 to $1,500.

Published on August 28th 2013 by under Medical Procedures.
Article was last reviewed on 28th August 2013.

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