Amniocentesis

What Is Amniocentesis?

Amniocentesis, also known as Amniotic Fluid Test is a test that detects chromosomal abnormalities in the fetus. A sample of amniotic fluid is taken from the amniotic sac (amnion) surrounding the unborn baby and its DNA is examined for genetic abnormalities. The fluid carries fetal tissue, it can assess whether the fetus has developed, or might develop a serious health condition or abnormality.

The fluid that surrounds the fetus in the womb - the amniotic fluid - has cells that the skin of the developing baby has shed, as well as his/her waste products. Each cell from the baby in the fluid contains their complete set of DNA (genetic information). Analyzing these cells helps the doctors assess the fetus' health and detect any potential problems.

If a problem is detected, it can sometimes be treated while the baby is still in the womb. The test is done early enough during the pregnancy so that if a serious abnormality is found, the parents have time to decide whether to terminate the pregnancy or see it through.

Older mothers, as well as those with a medical history, or women with inherited conditions have a higher risk of giving birth to offspring with a serious health condition or abnormality.

Amniocentesis can detect several conditions, such as:

• Down's syndrome - the result of an extra chromosome (trisomy-21) which affects the person's physical features, mental development, and ability to learn.
• Spina bífida and other neural tube defects
• Sickle cell anemia - the patient's red blood cells are of 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 a very rare condition.
• Trisomy 18 (Edward's syndrome) - causes severe physical and mental abnormalities. Trisomy-18 is an extra chromosome
• Fragile X (Martin Bell syndrome) - a genetic syndrome. The patient has physical and cognitive limitations, as well as emotional and behavioral features which can be mild to severe.
• Later on during the pregnancy it can detect infection, Rh incompatibility, lung maturity prediction, and decompression of polyhydramnios

Amniocentesis is increasingly used for the management of early rupture of the membranes during pregnancy - certain amniotic fluid inflammatory markers, such as amniotic fluid IL-6, can help the doctor decide whether to deliver the baby early.

Amniocentesis is usually done during the 15th week of pregnancy. The doctor inserts a needle into the amniotic sac and extracts a sample of fluid. Chorionic villus sampling (CVS) is an alternative procedure - tissue is taken from the vascular fingers (villi) of the chorion, a part of the placenta.

Amniocentesis is not a routine test, they are only carried out on mothers with a significant risk of having an offspring with a serious condition or abnormality. It is an invasive procedure with a slightly elevated risk of miscarriage (approximately 1%). The risks are greater if the test is carried out before 15 weeks.

In the USA, UK and many other nations, the mother will be offered genetic counseling.

Amniotic fluid has could become a key source of stem cells, with the advantage that they might be acceptable to individuals with ethical concerns regarding embryonic stem cells.

Sources: National Health Service (NHS), UK, National Institutes of Health (NIH), USA.