Diagnosis of chromosomal defects
Amniocentesis and CVS
- Diagnosis of fetal chromosomal abnormalities requires invasive testing by amniocentesis or chorionic villous sampling (CVS).
- Randomized studies have demonstrated that the risk of miscarriage from CVS in the first trimester is the same as for amniocentesis in the second trimester and is about 1%.
- Amniocentesis should not be performed before 16 weeks because with early amniocentesis the rate of miscarriage is about 2% higher and the incidence of talipes equinovarus is 1.5% higher than after first-trimester CVS or second-trimester amniocentesis.
- CVS should not be performed before 11 weeks because earlier CVS is associated with fetal transverse limb abnormalities, micrognathia and microglossia.
- Invasive tests should be carried out by appropriately trained and experienced operators. Recent evidence suggests that with such operators the risk of miscarriage may be as low as 1 in 1000.
Amniocentesis
Chorionic villus sampling