Types of screening tests

Prenatal screening tests include:

• First trimester screening tests. During your first trimester, your health care provider will offer a blood test and an ultrasound to measure the size of the clear space in the tissue at the back of a baby's neck (nuchal translucency). In Down syndrome and in certain other conditions, the nuchal translucency measurement is abnormally large.
• Second trimester screening tests. During your second trimester, your health care provider will offer another blood test called the quad screen. This test measures levels of four substances in your blood. Results indicate your risk of carrying a baby who has certain chromosomal conditions, such as Down syndrome. The test can also help detect neural tube defects — serious abnormalities of the brain or spinal cord.
• Prenatal cell-free DNA screening. This blood test examines fetal DNA in the maternal bloodstream to screen for the increased chance for specific chromosome problems, such as Down syndrome. This screening can also provide information about a baby's sex and rhesus (Rh) blood type.