Invasive Fetal TESTS
Invasive procedures are procedures designed to obtain samples from the placenta (CVS), amniotic fluid (amniocentesis) and fetal blood (cordocentesis) for analysis. They are offered to parents whose babies are thought to have an increased risk of having a chromosomal disorder such as Down syndrome (trisomy 21) or Edwards Syndrome (trisomy 18. It is also offered parents whose babies are at high risk for genetic disorders such as sickle cell, cystic fibrosis or thalassemia.
The samples from the placenta, amniotic fluid, and fetal blood all have the same genetic makeup as the baby and hence are used in diagnosing these conditions. The sample is sent to the lab for the specified test. The initial result for the three chromosomal abnormalities comes back in three to five working days while the final full karyotype result takes about two weeks. Based on the indication and the scan findings, further detailed genetics testing can be done on the same sample. Although the majority of patients are fine after the test, there is a small risk of miscarriage 0.5% associated with these procedures.
Chorionic Villus Sampling
Chorionic villus sampling (CVS) is an invasive prenatal test, performed between 11 and 14 weeks of the pregnancy. Under ultrasound guidance, a fine needle inserted through the mother’s abdomen into the placenta and a small placental sample (chorionic villi) are collected.
Amniocentesis is an invasive prenatal test available after 15 weeks of pregnancy. Under ultrasound guidance, a fine needle is inserted through the mother’s abdomen into the amniotic sac and a sample of amniotic fluid is collected and sent to the lab.
Cordocentesis is an invasive test carried out from 18 weeks of pregnancy. Under ultrasound guidance, a needle is passed through the mother’s abdomen under ultrasound guidance and a sample of the baby’s blood is taken from the cord. In addition to the indications mentioned above, this test is of particular value when the mother had a rhesus negative blood group.