Genetic Amniocentesis

Amniocentesis is a test that allows us to remove some of the amniotic fluid that surrounds the baby. The fluid can then be tested for certain types of birth defects or genetic disorders. Most commonly, amniocentesis is done to study the baby’s chromosomes. See the chromosome testing section for a list of some common reasons why chromosomes studies may be offered during pregnancy. Amniocentesis also allows for alpha fetoprotein (AFP) testing in the amniotic fluid. This is a more accurate test for problems like spina bifida than testing the AFP in the mother’s blood.

The amniocentesis test is done with ultrasound guidance. The physician places a needle through the mother’s abdomen and into the amniotic cavity (the fluid-filled sac that the baby floats in). A small amount of the fluid is then removed and sent to the laboratory. Most women do not find amniocentesis painful, although some women experience mild cramping with the procedure. While performing the ultrasound and preparing for the amniocentesis takes some time, the amniocentesis itself is usually performed in about one minute.

Like any invasive test, amniocentesis is associated with some risk. The risk for miscarriage associated with this test is usually said to be 1 in 200 (0.5%). However, we believe the actual risks at St. John’s Perinatal Center are lower than this (1/300 to 1/400). This risk is in addition to the background risk for miscarriage that every pregnancy faces (about 1-2% in the middle of the second trimester).

A doctor or genetic counselor will call you with your test results as soon as they are available. Chromosome results take about 7-10 days and AFP results take about 5-7 days. Other testing that may be done on the amniotic fluid, such as DNA testing, may take longer.