First trimester ultrasound
First trimester ultrasound screening is designed to evaluate for several chromosome problems, including Down syndrome. The ultra-sonographer will look at several different structures on your baby, including nuchal translucency (measurement of the amount of fluid underneath the skin at the back of the baby's neck), presence of the bone in the baby's nose and blood flow through a vessel called the ductus arteriosis. They also look at blood flow through the tricuspid valve in the baby's heart. Abnormalities in these specific areas can be associated with chromosome problems like Down syndrome.
First trimester biochemical
This is additional blood testing that looks at several pregnancy hormones in your blood. This blood testing may detect additional cases of Down syndrome, trisomy 13 or trisomy 18. This is an optional screen that can be performed in the first trimester.
Second trimester maternal serum
Second trimester maternal serum screening is designed to evaluate the risk for several chromosome problems, such as Down syndrome. It can also assess the risk for neural tube defects, such as spina bifida. This blood test can be performed between 15 and 22 weeks of pregnancy. This test in not recommended if a patient has already had screening in the first trimester of pregnancy.
Additional screening evaluating cell-free DNA from the placenta in a mother's blood is available in certain circumstances.