A technique, first used in 1882 to remove excess amniotic fluid, that involves extracting by centesis (inserting a hollow needle through the maternal abdominal wall into the uterus) a small amount of the fluid (usually about 1 cc for each week of pregnancy), and then analysing the fetal cells from the sample as a means of diagnosing fetal genetic abnormalities or determining the sex of the fetus. Requires the use of ultrasound to locate the fetus (see figure below). The technique does bring with it a slight risk of miscarriage, with estimates ranging from 1 in 200 to 1 in 400 procedures.
