Amniocentesis is a test carried out during pregnancy to diagnose any problems or serious health conditions your baby has developed or could develop.
Do you need an amniocentesis?
If your baby has a higher than normal chance of developing birth defects or other problems, you may want to have an amniocentesis. The following risk factors can increase the chances of health problems in your baby:
- You are aged 35 years or older.
- There is a history of inherited disorders in your family.
- You have had another child with an abnormality.
- Other screening tests, such as the combined first trimester screening test or the non-invasive prenatal test (NIPT), have shown the baby may have health problems. An amniocentesis can provide a clear diagnosis.
Talk to your doctor about whether an amniocentesis is right for you.
The risk of miscarriage after an amniocentesis is less than 1 in 200.
What happens during an amniocentesis?
Amniocentesis is usually carried out during weeks 15 to 20 of pregnancy. A needle is used to draw out about 15 to 30 mL (1 to 2 tablespoons) of amniotic fluid, the fluid that surrounds the baby in the uterus (womb). The doctor uses an ultrasound to guide the needle at all times. Amniotic fluid contains cells shed from the baby that can be examined and tested for a number of conditions.
Every baby cell in the amniotic fluid contains a complete set of the baby’s DNA. This provides information that can be used to diagnose any health or inherited problems the baby could develop.
What does an amniocentesis show?
Amniocentesis can be used to diagnose a range of potential problems.
Chromosomal conditions affect the chromosomes (parts of the body’s cells that carry genes). Some examples of chromosomal conditions include:
- Down syndrome — a condition that affects a person's physical appearance, mental development and learning ability; it is the result of an extra chromosome, known as trisomy-21.
- Edwards syndrome — a condition that causes severe physical and mental abnormalities; it is also the result of an extra chromosome, known as trisomy-18.
- Patow syndrome — a rare but serious condition where babies rarely survive for more than a few days; it is the result of an extra chromosome, known as trisomy-13.
Amniocentesis can also be used to check for inherited blood disorders, such as:
- Sickle cell anaemia — a condition where red blood cells (which carry oxygen around the body) are an unusual shape and texture.
- Thalassaemia — a condition that affects the body's ability to create red blood cells.
- Haemophilia — a condition that affects the blood's ability to clot.
Neural tube defects
Amniocentesis can test for neural tube defects. The neural tube is the tissue in early pregnancy that eventually develops into the spine and nervous system.
A neural tube defect can lead to conditions such as spina bifida, which can cause learning difficulties and paralysis (weakness) of the lower limbs.
Other genetic conditions
Other inherited genetic conditions may be tested for through amniocentesis, particularly if there is a known family history of the condition.
After an amniocentesis
Some women have mild cramping and lose a small amount of blood and/or amniotic fluid through the vagina after the procedure. This usually clears up without treatment over 24 to 48 hours. You should avoid strenuous activities or having sex for 48 hours after the amniocentesis.
Call your doctor immediately if you notice:
- severe pain or cramping
- persistent back pain or abdominal pain (lasting more than a few hours)
- fever or chills
- vaginal bleeding, or fluid leaking from your vagina
You will receive the results about 2 weeks after the amniocentesis. Most women's results are normal, but if there is any problem your obstetrician or a genetic counsellor (a healthcare professional trained in genetics) will talk to you and arrange any special care you or your baby may need.
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Last reviewed: July 2020