Typically, screening tests are used to identify pregnant women at risk for having a baby with Down syndrome. However, such tests do not yield a definitive diagnosis of the condition. At the present time, there are two commonly employed prenatal screening procedures: ultrasound and maternal serum screening tests.
An ultrasound of the fetus can be done during pregnancy and may produce signs suggesting Down syndrome. Ultrasound signals may show an increased amount of skin behind the neck, a condition referred to as "nuchal translucency." There may be other signs, including decreased femur length, heart defects, and gastrointestinal defects. While the aforementioned ultrasound signals may tend to suggest Down syndrome, the definitive diagnosis cannot be based solely on the ultrasound findings. Ultrasound findings only suggest a slightly higher risk that a fetus may have Down syndrome. If there are positive ultrasound findings, the attending physician may recommend additional testing to confirm the diagnosis.