Genetics Northern California



Amniocentesis is a procedure done between 15 and 20 weeks to identify genetic conditions in a developing baby (fetus).  The procedure takes a small sample of fluid from the pregnancy. Fetal chromosomes from the sample are studied in the laboratory to check for chromosome conditions. A substance called AFP is measured to check for neural tube defects and abdominal wall defects. 

Amniocentesis fact sheet: Amniocentesis

How amniocentesis is done:  A thin needle is passed through your abdomen (belly) and into the amniotic sac.  Ultrasound is used to guide the needle so it does not touch the fetus. A small amount of the fluid is removed. It usually takes about a minute or less to get the sample.   

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. A genetic counselor calls you as soon as they are available. The results can accurately tell whether or not the baby has a chromosome condition, such as Down syndrome or trisomy 18. The result also includes information about the chance for an open neural tube defect or abdominal wall defect. Most amniocentesis results are normal. However, if the result shows that your baby has a birth defect or chromosome condition, you will be given information about the specific problem and how it may affect the baby. All available treatments and options for continuing or ending the pregnancy will also be discussed.


Last reviewed: April 2020

Reviewed by: Kimberly Barr, LCGC  - Kaiser Permanente NCAL Regional Genetics