These screenings are similar to the first trimester screen, but they do not include an ultrasound, so they are less accurate. They can be done between 15 and 22 weeks.  There is a triple screen (measuring AFP, HCG, and Estriol) that looks for risk of Down syndrome, Trisomy 18, and neural tube defects. This test is 69% accurate in detecting Down syndrome (2). There is also a quad screen (measuring AFP, HCG, estriol, and inhibin-A) that is also looking for the risk of Down syndrome, Trisomy 18, and neural tube defects. This test is 81% accurate in detecting Down syndrome (2).