Screening tests during pregnancy
Screening for Down syndrome is offered as a routine part of prenatal care. Although screening tests aren't perfect, they can help you make decisions about more-specific diagnostic tests and the course of the pregnancy.
Various screening tests can help identify whether you have a high risk of carrying a baby with Down syndrome, but they can't identify whether your baby has Down syndrome. Screening tests include the first trimester combined test, the integrated screening test and the cell-free fetal DNA analysis.
The first trimester combined test
The first trimester combined test, which is done in two steps, includes:
Blood test. This blood test measures the levels of pregnancy-associated plasma protein-A (PAPP-A) and the pregnancy hormone known as human chorionic gonadotropin (HCG). Abnormal levels of PAPP-A and HCG may indicate a problem with the baby.
Ultrasound. Ultrasound is used to measure a specific area on the back of your baby's neck. This is known as a nuchal translucency screening test. When abnormalities are present, more fluid than usual tends to collect in this neck tissue.
Using your age and the results of the blood test and the ultrasound, your health care provider can estimate your risk of having a baby with Down syndrome.