Triple or quadruple screening test.

Doctors check your blood for hormones and proteins that come from your baby or your placenta, the organ that brings him oxygen and nutrients. The test can look for three different substances (triple screening) or four (quadruple screening). Certain amounts of these mean your baby has a higher chance of having a birth defect or a genetic disease. This test happens in thesecond trimester, usually at 15 to 20 weeks.