What is Amniocentesis?

Amniocentesis, by definition, is the procedure of obtaining a sample from the amniotic fluid inside the amniotic sac, which is the water sac surrounding the baby. The steps of the procedure are simple and short. After sterile conditions are ensured, a fine needle is inserted through the abdomen under ultrasound guidance, passing through the abdominal layers, then through the uterine wall, and reaching the baby’s amniotic sac. The side where only the sac is seen and not the baby is preferred. Even if the needle touches the baby, it usually does not cause any harmful effect. The sample taken from the sac with the help of a syringe is sent in a sterile way to the laboratory for examination. Although the procedure is simple, it is important that the doctor performing it has received special training.

Amniocentesis, which is usually performed when there is suspicion of a chromosomal abnormality, can actually provide other information as well. Tests can be performed on the obtained fluid to show the maturity of the baby’s lungs, and it can also indicate whether an infection the mother has had has passed to the baby.

The amniotic fluid sample taken for chromosomal abnormality screening is valuable because of the epithelial cells belonging to the baby contained in it. These cells are separated through special processes and brought to the stage of proliferation in a culture medium. In this way, the chromosomal structure of the dividing cell can be determined. The result is definitive most of the time. An exceptional condition is mosaicism, in which some of the cells show a normal chromosomal structure while others show an abnormal structure. Rarely, the culture may fail due to inadequacies in the culture environment or because of the low number of cells in the sample taken. In such cases, the procedure may need to be repeated in order to obtain a result.

Amniocentesis is not an entirely harmless procedure. One in 200 pregnancies undergoing amniocentesis may result in miscarriage due to the procedure. For this reason, doctors recommend this procedure to their high-risk patients. If the results of the screening tests show high risk, if the nuchal translucency measurement is increased, or if there is a finding on ultrasound suggesting a genetic abnormality, detailed information is provided to the expectant parents. After the expectant mother and father read and sign the informed consent form, the procedure is carried out. Amniocentesis is performed between the 16th and 19th weeks of pregnancy. Results can be obtained within a few days using a method called the FISH test, but the more reliable culture results can be obtained after approximately 20 days of waiting. The procedure is painless and does not require anesthesia. If, as a result of the procedure, a genetic abnormality compatible with life is detected, the pregnancy may be terminated with the approval of an ethics committee as well as the family’s request for termination.