Amniocentesis

Amniocentesis is a procedure that can be used to accurately detect genetic disorders and certain birth defects (neural tube defects) in an unborn baby (fetus). It involves the removal and examination of some fluid and cells inside the amniotic sac that surrounds the developing fetus. It is often performed in the mid second trimester. It is always performed together with the ultrasound to help guide the needle correctly.

Amniocentesis tests for very specific genetic disorders based upon significant family and individual risk factors. Genetic disorders may be caused by: abnormalities in the chromosomes, biochemical defects (abnormalities in body chemistry), multiple factors (several abnormal genes and gene/environment interactions). In addition, amniocentesis can also test for presence of neural tube defects (open spinal defects, spina bifida) and/or abdominal wall defects. However, many genetic disorders still cannot be detected prenatally by any means.

During the amniocentesis, amniotic fluid is obtained through a needle from the amniotic sac that surrounds the fetus. The mother's abdomen is cleansed. Under ultrasound guidance, a sterile needle is inserted through the abdominal wall into the amniotic sac. Approximately 20 mL (4 tsp) of amniotic fluid is withdrawn and taken to the cytogenics laboratory. The fetal cells will then be removed and grown for chromosomal or biochemical analysis. Some of the fluid is sent to a specific laboratory to be tested for evidence of the development of the brain or spinal cord. It usually takes 2 weeks to complete the analysis for chromosomal abnormalities and 1 to 2 weeks to complete the analysis for neural tube defects.

The risk of a complication from an amniocentesis is approximately 1 per 200-300 procedures. The complications include, but are not limited to bleeding, infection, premature rupture of the membranes, and miscarriage or fetal death.

The procedure causes mild discomfort. A local anesthesia may be used to minimize this pain. The sensation is similar to that caused by having an IV inserted in the arm. Uterine cramping is also likely to occur, which resembles menstrual cramps. The cramps associated with amniocentesis quickly resolve after the procedure is done.