How is an Amniocentesis performed?
What is amniocentesis?
Amniocentesis is a procedure which consists in removing a small amount of amniotic fluid, which is the liquid that holds the fetus during pregnancy.
In the uterus, the fetus is surrounded by a membrane which forms a sac containing the amniotic fluid. This sterile liquid, mostly made up of water and mineral salts, contains fetal cells.
The fluid sample is removed using a very thin needle attached to a syringe. This needle is inserted through the mother’s abdominal wall to reach the amniotic cavity.
Amniocentesis is performed by a doctor specialized in fetal medicine who will accompany you throughout the procedure.
It is pain-free and entirely ultrasound-guided. Local anesthesia at the injection site is not required. During amniocentesis, the fetus does not feel anything and the extreme precision offered by ultrasound guidance means the doctor can remain at a safe distance from the baby at all times.
What is the purpose of amniocentesis?
The small sample of amniotic fluid contains fetal cells which will be analyzed in a specialized laboratory accredited by the French Biomedicine Agency.
This analysis is used to:
- Perform a fetal karyotype (verification of the number of chromosomes of the fetus) in order to search for chromosomal abnormalities;
- Search for genetic abnormalities, such as the abnormality which causes cystic fibrosis or fragile X syndrome (a genetic disease causing intellectual disability);
- Identify any biochemical abnormalities, for instance in cases of spina bifida (abnormal development of the spine in which the vertebrae don’t close properly);
- Screen for viruses in the amniotic fluid (for instance following a CMV or toxoplasmosis seroconversion).
However, this procedure does not detect all potential diseases.
When should amniocentesis be performed?
Amniocentesis is generally performed after three months of pregnancy (after 15 weeks following the last menstrual period). However, it can be done up until the end of pregnancy if necessary.
You will systematically be asked to undergo amniocentesis if you are on medication (aspirin, anticoagulants) and if you have allergies (iodine).
What should you expect afterwards?
After the procedure, you will be given an antispasmodic medication. A blood test may be performed to make sure the fluid sample has not been contaminated by your blood.
We recommend that you rest for 48 hours afterwards and take pain killers if necessary. You will be placed on sick leave and receive a prescription for pain killers.
For a few hours, you might feel cramping or pain where the needle was introduced. This is normal and no cause for concern.
Please note: If your blood is Rh negative and your fetus’s is Rh positive or undetermined, we will prescribe a 200 mcg injection of Rophylac® to be used as a prophylaxis against alloimmunization.
Results may be obtained in two separate phases, depending on the type of analyses performed:
- When screening for chromosomal abnormalities, data on trisomy 21, 18 and 13 are available within two to three days.
- The complete karyotype analysis can take two to three weeks because it requires a cell culture (multiplication of cells in a nutrient-enriched medium). Results may be delayed if the cells take longer to develop.
In rare cases, the cell culture is unsuccessful, making it necessary to discuss the possibility of a second amniocentesis. You will come in for a consultation to receive your results.
You must go to an emergency service specializing in gynecology near your home or contact the 24/7 emergency department of the American Hospital of Paris at +33 1 46 41 25 25 if you experience any of the following after the procedure:
- Loss of amniotic fluid
- Contraction-like pain