Amniocentesis is a technique by which chromosomal or genetic disorder in a developing foetus can be detected. This is based on the chromosomalíkaryotype pattern in the cells found the amniotic fluid surrounding the developing foetus. Amniotic fluid contains cells and molecules shed by the foetus. The chromosomes of foetal cells can also be used to find out the sex of the foetus and abnormalities if any.
So, if an abnormality is found, the mother can start the treatment or get the foetus aborted.