Amniocentesis is a invasive antenatal test that is performed to detect fetal abnormalities, in particular due to chromosomal problems, such as Down’s syndrome.Chromosomes carry genes that pass certain characteristics from parents to their children. When there are too many or too few chromosomes, or there is a defect in a chromosome, birth defects usually occur.

Amniocentesis is usually done if there is a high risk of fetal abnormalities following serum screening tests or ultrasound scans. These tests are usually offered to women who have an increased chance of having a baby with a disorder eg women over 35 years old, women who have had a previous Down Syndrome child or other chromosomal disorders, or women who know that they or their baby’s father have an unusual chromosomal arrangement. It is not usually offered on a routine basis.

During amniocentesis, a needle in inserted through the women’s abdomen into the amniotic sac under ultrasound guidance and a sample of amniotic fluid is taken and sent to the laboratory for analysis.