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Amniotic fluid is the thin watery substance that surrounds the developing fetus in the uterus/womb. Amniocentesis involves removing a small amount (about 4 teaspoons) of this fluid with a needle, for testing in the lab. This test can be done after the 15th week of pregnancy.  More information can be found below and on the Prenatal Genetic Screening Program website.  

What it detects

What can Amniocentesis detect?

Amniocentesis is a specific test that is able to tell you if your baby has a normal number of chromosomes (46). It can find Down syndrome and other major chromosome abnormalities. A second test is done to measure the amount of alpha-fetoprotein (AFP) in the amniotic fluid. A higher than normal amount may suggest the possibility of a neural tube defect, such as spina bifida. Normal results can take up to 3 weeks. Concerns are usually identified and given to your doctor or midwife within 10-14 days.
If there is a family history of a known problem, other special tests may be done on the amniocentesis sample. You need to discuss this with your doctor or midwife who will refer you to Medical Genetics for additional tests in advance of your procedure.
Five in 100 women have a chance of having a baby with a major birth defect that can be found during the first year of life. The most common defects are cleft lip and palate, clubfeet, heart defects and mental retardation. The results from amniocentesis, CVS or fetal blood sampling will indicate whether or not there are chromosome abnormalities or neural tube defects, but will not be able to rule out other abnormalities.

What are the risks

 What are the risks involved in amniocentesis?
  • Miscarriage: It is important to note that the risk of miscarriage unrelated to any procedure is about 6 in 100 at nine to twelve weeks of pregnancy, decreasing to 1 in 100 by the fifteenth week of pregnancy. Following amniocentesis, there is an additional risk that 1-2 in 200 women will have a miscarriage (1-2 in 100 for twin pregnancy). Also, 2 in 100 women will have problems, such as amniotic fluid leakage or bleeding.
  • Damage to the Fetus: It is rare for the needle to touch the fetus because ultrasound is used as a guide, and the needle can be moved in another direction. Sometimes amniocentesis must be repeated because the cells do not grow in the laboratory, or there are not enough cells in the fluid sample.
  • Bleeding, Cramping or Infection: Cramping during or following the procedure is not uncommon and usually gets better with rest. Small amounts of bleeding or amniotic fluid leakage may occur following the procedure. Infection following amniocentesis rarely occurs, and would likely begin to show with a fever and flu-like symptoms.
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