Is a prenatal diagnostic test usually performed between 16th and 20th weeks of pregnancy. The procedure involves passing a needle through the skin of the mother and through the wall of the uterus to remove a small sample of amniotic fluid that surrounds and protects the baby during pregnancy.
As amniotic fluid contains fetal cells and various chemical produced by the baby, it can be analysed to investigate an increased risk for genetic and chromosomal disorders and neural tube defects (e.g Down syndrome, cystic fibrosis, spina bifida).
Since it is quite invasive and carries a small risk of miscarriage, it is usually recommended only when mother's age, medical history, family history or a prenatal screening test suggest an increased risk of chromosomal abnormalities or birth defects.
Amniocentesis can also be used later to assess for uterine infections (if membranes are ruptured prematurely), to determine severity of fetal anemia in cases with Rh disease, or to assess lung maturity.
Amniocentesis does not detect birth defects such as heart malformations or a cleft lip or palate. However, many structural defects can be picked-up on the ultrasound routinely done when having an amniocentesis.