The quad screen (sometimes referred to as the quadruple screen, AFP4, or multiple marker) is a blood test that can tell you whether your baby is at an increased risk for certain problems. The conditions it screens for are Down syndrome and trisomy 18, which are chromosomal abnormalities, as well as neural tube defects, such as spina bifida. The quad screen is done in the second trimester, usually between 15 and 18 weeks of pregnancy. Ideally, the test should be performed in conjunction with first-trimester screening tests. This combination is known as integrated or sequential screening. But if you miss the opportunity to start your screening in the first trimester, the quad screen alone can still give you some good information. These screening tests help you assess your baby's chances of having certain genetic diseases and birth defects. The results can help you decide whether to have amniocentesis, an invasive diagnostic test, to find out for sure about your baby's condition.Screening tests tell you how likely it is that your baby has a condition, but only a diagnostic test like amniocentesis tells you whether your baby actually has the condition. While the quad screen carries no risk for the mom or baby, amniocentesis does have a small risk of miscarriage.