Which diagnostic tests are required during this time?

Second-trimester screening includes the following tests: - The “quad” or “quadruple” blood test measures the levels of four different substances in your blood. The quad test screens for Down syndrome, Edwards syndrome (trisomy 18), and NTDs. It is done between 15 weeks and 22 weeks of pregnancy. - An ultrasound exam done between 18 weeks and 22 weeks of pregnancy checks for major physical defects in the brain and spine, facial features, abdomen, heart, and limbs.