Genetics Northern California



Amniocentesis is a test done during the second trimester of pregnancy, usually between 15 and 20 weeks. It is a diagnostic procedure that can identify genetic conditions in the developing baby (fetus).  It involves removing a sample of the fluid from your pregnancy. The sample is analyzed to check for chromosome abnormalities in the fetus.

Here's an easy-to-read handout on amniocentesis: Amniocentesis

How amniocentesis is done:  Using ultrasound guidance, a thin needle is inserted through your abdomen (belly) and into the amniotic sac.  The ultrasound makes sure the needle does not touch the fetus. A small amount of the amniotic fluid is removed. It usually takes about a minute or less to get the sample.   

Cells from the developing baby are floating in the amniotic fluid. These cells are processed in the laboratory, and the fetal chromosomes are studied. The amount of AFP in the amniotic fluid is also measured. AFP helps look for neural tube defects and abdominal wall defects. 

Risk: The risk for miscarriage due to an amniocentesis procedure is 1 in 500 or less. 

Amniocentesis results: Results are usually available within 14 days. The results indicate whether or not the baby has a chromosome abnormality, such as Down syndrome or trisomy 18. The result also includes information about the risk for an open neural tube defect or abdominal wall defect.

A genetic counselor calls with results as soon as they are available. Most amniocentesis results are normal. However, testing will sometimes find a chromosomal abnormality or other serious problem.  Chromosome abnormalities are not curable. If amniocentesis results show that your baby has a birth defect or chromosome abnormality, you are given information about the specific problem and how it may affect the baby. This can include discussions with your genetic counselor, your doctor, nurse practitioner or nurse midwife, and possibly other specialists such as a geneticist or perinatologist. All available treatments and options for continuing or ending the pregnancy are discussed.


Last reviewed: December 11, 2017

Reviewed by: Kimberly Barr, LCGC