How do doctors diagnose Down syndrome?

Doctors can diagnose Down syndrome before a baby is born or at birth. People may choose to participate in counseling or join a support group if they find out the baby they are carrying has Down syndrome.

In prenatal (before birth) tests called screenings, a doctor may use blood tests and ultrasound (imaging test) to look for “markers” that suggest Down syndrome may be present.

Other prenatal screenings doctors use to diagnose Down syndrome include amniocentesis and chorionic villus sampling (CVS).

In these tests, a doctor removes a sample of cells from the part of the womb called the placenta (CVS), or the fluid surrounding the baby (amniocentesis), to look for abnormal chromosomes. Parents can choose whether or not to have these prenatal screenings.

At birth, doctors perform a physical exam to look for the physical signs of Down syndrome. To confirm the diagnosis, doctors use a blood test called a karyotype. In this test, the doctor takes a small sample of blood and studies it under a microscope to see if an extra amount of chromosome 21 is present.

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