Prenatal Diagnosis

Amniocentesis and Chorionic Villus Sampling (CVS) Including FISH Results Within 24-48 Hours




Amniocentesis and Chorionic villous sampling are the definitive diagnostic tests for pregnancies at high risk for chromosome and other genetic abnormalities such as Down syndrome. These tests confirm or exclude a chromosomal or genetic abnormality in a high risk fetus.


The indications for testing include high risk result from the nuchal translucency scan, diagnosis of fetal abnormalities on the routine morphology scan, advanced maternal age and a family history of inherited genetic conditions. 


Amniocentesis involves collecting a sample of amniotic fluid from the pregnancy sac around the baby. A fine needle is used under ultrasound guidance to collect this sample. Generally this test is performed between 15 - 19 weeks of pregnancy and involves a small risk of miscarriage.


Chorionic Villous Sampling (CVS) is performed earlier in the first trimester of pregnancy for chromosomal or genetic diagnosis. Under ultrasound guidance, a biopsy of the placenta is obtained through the abdominal wall. This procedure can be performed between 11 - 14 weeks of pregnancy and also carries a small risk of miscarriage.


Samples obtained by amniocentesis or CVS are sent for full chromosome analysis (full karyotype). These results generally take 12-14 days to be completed. An additional technique called RAPID FISH (Fluorescent in-situ hybridization) is also available on the same sample to provide information regarding the number of chromosomes in chromosome 13, 18, 21(Down syndrome), X and Y groups within 24-48 hours.