Amniocentesis

What is amniocentesis for?

Amniocentesis is used to diagnose chromosome abnormalities such as Down syndrome and Trisomy 18. It is also used to determine the risks for having an open spina bifida and can also be used to test for other genetic conditions. This is offered only when a risk for having a baby with a genetic condition is identified.

What does the procedure involve?

Amniocentesis is the drawing of a small amount of fluid from the fluid around the baby. The procedure takes approximately 5 minutes with a resting period of 30 minutes after.

At the time of amniocentesis, an obstetrician performs an ultrasound to check the gestational age of the baby, the heartbeat and the amount of amniotic fluid. Using the ultrasound as a guide, the obstetrician inserts a fine needle through the abdominal wall and into the uterus. Care is taken to avoid placing the needle near the baby.

Approximately 15 ml (about a tablespoon) of amniotic fluid is withdrawn from the fluid surrounding the developing baby. It is not harmful to take this fluid because it is the urine of the baby which the baby will replace within a few hours.

Some women say that amniocentesis doesn’t hurt at all; others feel slight pressure and a mentrual-like cramp when the needle enters the uterus and the fluid is being withdrawn. After the procedure, some women experience cramping, spotting, or leakage of amniotic fluid.

Most doctors recommend that a woman take it easy for several hours after amniocentesis, avoiding physical stresses such as lifting and prolonged standing.

Amniotic fluid contains fetal cells and fluid produced by the fetus. The fetal cells are removed from the sample and grown in the laboratory for 10 to 12 days. The cells are then tested to determine whether or not there is a chromosome abnormality. There are other tests that can be done on the sample if indicated. DNA and biochemical testing may be performed when the fetus is at risk for a particular genetic disorder.

The amniotic fluid can also be used to measure alpha fetoprotein (AFP), which may indicate whether or not there is an open neural tube defect.

When can amniocentesis be done?

Amniocentesis is done after 15.5 weeks from the last menstrual period.

When will the results be available?

The chromosome results from amniocentesis are usually available within three weeks. The laboratory will notify you referring doctor, midwife or genetic counsellor as soon as the analysis is complete. However, at Mount Sinai hospital, using a technique called QF-PCR, we can provide information regarding chromosomes 13, 18, 21, X & Y and the gender of the baby within 24-48 hours.

What else can amniocentesis tell me?

In addition to detecting Down Syndrome, amniocentesis can detect other chromosome abnormalities. In cases where there is a family history of a specific genetic condition, special genetic testing can also be ordered in addition to routine chromosome testing.

The amniotic fluid can also be used to measure alpha fetoprotein (AFP). AFP is a protein produced by the fetus and is often elevated where there is an open neural tube defect.

How accurate is this test?

The accuracy of amniocentesis in chromosome analysis is 99.9%.

What are advantages of amniocentesis?

Amniocentesis is the safest and most accurate diagnostic test currently available to inform you whether or not your baby has a chromosome problem.

What are the risks associated with amniocentesis?

Miscarriage: The natural rate of miscarriage after 16 weeks is approximately 3 per cent. The additional risk due to amniocentesis ranges from 0.1-0.3% (1/300-1/900). .

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 nearest emergency room.

Infection: Infection following the procedure is extremely rare. However if you develop fever, chills, cramps or bleeding call your doctor immediately or go to the nearest emergency room.

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

What are the limitations of amniocentesis?

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.
Normal amniocentesis results do not guarantee a normal pregnancy. Amniocentesis tells a mother whether or not her baby has a chromosome abnormality. Special testing has to be requested if a specific gene has to be tested for a genetic condition.
Amniocentesis, as well as CVS, cannot provide information about all aspects of a baby’s development, for example mental retardation. For every pregnancy, regardless of the mother’s age, there is a chance that a baby will have a birth defect that cannot be detected before birth. No test exists which will guarantee a normal baby.

What if I am Rh negative?

Rhogam immunoglobulin injections are given at the time of the procedure to mothers with Rh negative blood type to prevent development of antibodies which could harm the baby.

Special Pregnancy Program

Referrals »

Fetal Medicine: 416-586-4800 x 7756
Fax: 416-586-3216

Maternal Medicine: 416-586-4800 x 7000
Fax: 416-586-5109

Main clinic hours: Monday to Friday, 8am to 4pm

Prenatal Diagnosis & Medical Genetics

Referrals »

phone: 416-586-4800 x 4523
fax numbers:
416-586-4723 or 416-586-8384

Perinatal Mental Health

Referrals »

Phone: 416-586-4800 x 8325
Fax: 416-586-8596