How accurate is the first trimester screening?
The blood test alone (without the ultrasound NT measurement) identifies 68% of Down syndrome and 90% of Trisomy 18 fetuses. The blood test and ultrasound when used in combination has a 91% detection rate for Down syndrome and 97% detection rate for Trisomy 18. The test can also pick up 40% of fetuses with heart defects and some other birth defects.
