 Down syndrome is the second most common chromosomal abnormality associated with increased nuchal translucency, after Turner syndrome (45,X).Until recently, the only reliable ways to determine if the fetus has a chromosomal abnormality was to have an invasive test such as amniocentesis or chorionic villus sampling, but such tests carry a risk of causing a miscarriage estimated variously as ranging between 1% or 0.06%.Based on maternal age, some countries offer invasive testing to women over 35; others to the oldest 5% of pregnant women.