Amniocentesis genetic diagnosis. Animation of the process by which foetuses are tested for medical conditions whilst still in the womb. The aim of this is to detect birth defects including genetic diseases and chromosome abnormalities. A sample of the amniotic fluid, together with the foetal cells present in it, is obtained by inserting a needle into the uterine cavity (upper left). A syringe is attached to the needle and amniotic fluid is withdrawn. This amniotic fluid is then centrifuged (upper centre) to obtain the cells. The DNA (deoxyribonucleic acid, bottom right) is extracted from the cells and analysed. Chromosomal abnormalities that can be diagnosed are trisomy (including Down syndrome), monosomy (such as Turner syndrome) or other aberrations. The final stage of the animation shows another form of prenatal diagnosis, known as chorionic villus sampling, with the fluid for analysis obtained from the placental villi (lower left).