Amniocentesis is a procedure in which a small amount of amniotic fluid surrounding the baby is removed via a fine needle passed through the mother’s abdomen and tested for chromosomal abnormalities like Down syndrome. Amniocentesis can also be used to test for neural tube defects (conditions where the developing spine fails to close properly).
The safest time to have an amniocentesis is between weeks 16 to 20 of the pregnancy. However, due to its invasive nature, amniocentesis carries the risk of miscarriage (0.2-0.3%) and is recommended only for women whose fetus has significant risk of genetic disorders.
It takes a few days to about 2 weeks for the results to be available. If a disorder is diagnosed, you will be given the relevant information and ample opportunities to discuss with us what the available options are.
Chorionic villus sampling (CVS) is a prenatal test that also helps detect chromosomal abnormalities and a host of other genetic disorders including cystic fibrosis, sickle cell disease and thalassemia. Cells are taken from the placenta via a needle inserted through the abdomen under ultrasound guidance and sent to a lab for genetic analysis.
The main advantage of CVS over amniocentesis is that it can be performed earlier—generally between 11 and 12 weeks of pregnancy so you can find out about your baby’s condition sooner. The miscarriage rate associated with CVS is higher (0.5 to 1%) and the risk of fetal limb abnormalities is minimised when performed after 11 weeks.
However, unlike amniocentesis, CVS cannot test for neural tube defects as no amniotic fluid is collected. Results are usually available in a few days to about 2 weeks.