Amniocentesis is a medical procedure in which a small amount of amniotic fluid is removed from the amniotic sac surrounding the fetus in the uterus

The test is regularly performed at about 16 weeks of gestation (recommended between 14 and 22 weeks). A sample of amniotic fluid (20-40 ml) is removed transabdominally with ultrasound guidance. The cells of the fluid are cultured and karyotyped. In addition to detecting Down syndrome, this technique can also be used for prenatal diagnosis in families with known chromosomal rearrangements or in pregnancies with abnormal ultrasound.

Most of the amniotic fluid cells originate from the fetus and include fibroblasts, epithelial cells and amniocytes. Cells suitable for genetic analysis are fibroblasts and amniocytes, and the preparation of chromosomes from these cells gives a clear picture of the chromosomes for microscopic observation.