Prenatal Tests

Prenatal Screening Tests versus Diagnostic Tests

Prenatal diagnostic testing is used to determine whether your baby has a chromosomal abnormality. The most common types of prenatal diagnostic tests available are chorionic villus sampling (often simply called “CVS”) and amniocentesis (often simply called “amnio”).

We are experienced at performing chorionic villus sampling and amniocentesis at Northern Ultrasound for Women.

Chorionic villus sampling and amniocentesis are different from prenatal screening tests such as nuchal translucency scans.

Prenatal diagnostic testing is considered an invasive way of determining the presence or absence of a chromosome abnormality. These tests involve putting a needle into either the placenta or amniotic sac of the developing pregnancy and hence they are associated with an increased risk of miscarriage. These tests are usually performed only in certain situations.

Prenatal diagnostic testing (CVS and amniocentesis) provide a definitive diagnosis of a chromosome abnormality.

For example, CVS/amniocentesis will tell us either

• the baby definitely does not have a chromosome abnormality, or
• the baby definitely has a chromosome abnormality.

This is different from the results of combined first trimester screening (nuchal translucency scan and specific blood tests). First trimester screening is a “screening” test only and does not provide a definitive answer. First trimester screening simply tells us if the risk of your baby having a chromosome abnormality is high or low.

First trimester screening gives us an indication of whether we should worry about your baby based on these results. If we are worried about your baby, prenatal diagnostic testing will be offered.