Amniocentesis is used to help diagnose chromosome abnormalities such as Down syndrome. It is also used to determine risks for open spina bifida in certain cases.

Amniotic fluid can also be used to test for other genetic conditions. This is offered only when a genetic counsellor and geneticist identify a risk for a genetic condition after obtaining a detailed family history.

Amniocentesis is an invasive procedure performed at Mount Sinai Hospital on an out-patient basis. The procedure takes approximately 10 minutes with a resting period of 20 minutes after.

It is usually done after 15.5 weeks from the last menstrual period. An ultrasound examination is done to identify the position of the placenta and the developing baby.


Using the ultrasound as a guide, an obstetrician inserts a fine needle through the abdominal wall and into the uterus.

Approximately 15 ml (about a tablespoon) of amniotic fluid is withdrawn from the surroundings of the developing baby. The procedure lasts only a few minutes and cramping may occur.

Risks/Limitations of Amniocentesis

The natural rate of miscarriage after 16 weeks is approximately 3%. The additional risk due to amniocentesis is about 0.5% (1/200), making the total risk about 3.5%.

Leakage of amniotic fluid, spotting or cramping
These problems may occur during the first 12 hours following amniocentesis and usually settle with rest. If these problems continue or become progressively worse, call your doctor or go to the emergency room of a hospital close to where you live.

Infection following the procedure is extremely rare. However if you develop fever, have chills, cramps or bleeding call your doctor immediately.

Injury to baby
There is a very small risk of the needle touching the baby.

Repeat testing
Rarely, a repeat amniocentesis may be required if sufficient fluid cannot be obtained at the time of amniocentesis or if a technical problem occurs in the laboratory. This does not necessarily mean there is a problem with the pregnancy.

Amniocentesis does not guarantee a normal pregnancy

Amniocentesis tells a mother whether or not her baby has a major chromosome abnormality, but special testing has to be requested if a specific gene has to be tested for a genetic condition.

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