Amniocentesis

Amniotic fluid obtained via amniocentesis provides a source of fetal material that can be used for prenatal diagnostic testing. Amniocentesis is performed after week 15 of gestation. Ultrasound is performed before and during the amniocentesis to guide the needle. The very thin needle is put into the uterus through the abdomen.

Amniocentesis has a 1% associated risk of spontaneous abortion. It is therefore only offered to couples when there is an increased risk of a chromosomal abnormality or another genetic disorder.

20-30 mL of amniotic fluid is obtained in a typical amniocentesis procedure. The fluid consists of a cellular component and supernatant component which can be separated using a centrifuge. The cellular component can be used for prenatal genetic testing e.g., using DNA methods or chromosome analysis. The supernatant component can be used for certain biochemical studies mostly for determination of alpha-fetoprotein (AFP) level as a screen for neural tube defect.

Figure 1: Amniocentesis. The ultrasound guide the physician in inserting the needle into the amniotic sac.