Amniocentesis: What you really need to know

Amniocentesis, or the amniotic fluid test, is an invasive prenatal diagnostic test that detects chromosomal abnormalities in the fetus.

Those with a higher risk of giving birth to children with a serious health condition or abnormality include:

women aged over 35 years

women with a medical history of an inherited condition such as sickle cell anemia or muscular dystrophy

women who have undergone a previous pregnancy with genetic problems such as Down’s syndrome

The amniocentesis test is 98 to 99 percent accurate for testing chromosomal abnormalities, neural tube defects, and genetic disorders. Around 200,000 tests are carried out in the United States (U.S.) each year.

What is amniocentesis?

Amniocentesis is an invasive diagnostic procedure in which a doctor examines the genetic materials in a fetus’ surrounding amniotic fluid.

Amniocentesis is often carried out between 15 and 18 weeks of gestation.

The amniotic sac, or amnion, surrounds the fetus during pregnancy. The sac contains a fluid called amniotic fluid. The fetus is completely submerged in this fluid.

In the test, an ultrasound guides a 22-gauge spinal needle to a safe place in the amniotic sac.

The needle extracts between 10 and 20 milliliters (ml) of amniotic fluid from the sac, and the fluid is sent for testing. This represents about 1 ml of fluid per week of gestation.

The whole procedure takes around 45 minutes, but the extraction of the fluid itself takes less than 5 minutes.

How is the fluid analyzed?

In the lab, the fetal DNA is examined for genetic abnormalities.

The fluid carries fetal tissue, including skin cells and fetal waste products, so it can be used to assess whether the fetus is developing normally, or if it is at risk of developing a serious health condition or abnormality.

Each cell from the fetus contains a complete set of DNA, or genetic information.

[Amniocentesis can help detect Down's syndrome]
Amniocentesis can help in diagnosing Down syndrome at an early stage of pregnancy.

Amniocentesis may detect Rh disease, which can lead to severe anemia in the fetus. If so, a blood transfusion may be possible.

If there is a significant problem, the parents may decide to terminate the pregnancy.

Amniocentesis can detect several conditions.

These include:

Down syndrome: An extra chromosome, known as trisomy-21, can affect a person’s physical features, mental development, and ability to learn.

Sickle cell anemia: The red blood cells have an unusual shape or texture. Red blood cells carry oxygen around the body.

Thalassemia: The body’s ability to create red blood cells is poor.

Trisomy 13 (Patau’s syndrome): The extra chromosome, trisomy 13, causes a serious condition in which the newborn survives just for a few days. It is very rare.

Trisomy 18, or Edward’s syndrome: Trisomy-18 is an extra chromosome that causes severe physical and mental abnormalities.

Fragile X, or Martin-Bell syndrome: This is a genetic syndrome that causes physical, cognitive, emotional, and behavioral challenges, which can range from mild to severe.

Spina bifida and other neural tube defects.

In the later stages of pregnancy, amniocentesis can detect infection, Rh incompatibility, lung maturity prediction, and decompression of polyhydramnios.

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