Anyone who is pregnant can choose to have a diagnostic test, regardless of the risk of chromosomal abnormalities. These tests can count the chromosomes and look for any differences, including those that are less common. The two types of diagnostic tests are chorionic villus sampling (CVS) and amniocentesis.

How are chromosomal abnormalities detected?

Prenatal diagnosis of chromosomal abnormalities is currently accomplished by invasive techniques, such as amniocentesis and chorionic villus sampling (CVS). CVS is performed in the first trimester from 10 through 13 weeks' gestation, whereas amniocentesis can be performed starting at 15 weeks' gestation.

When do you test for chromosomal abnormalities?

Your blood is tested for hormones from your placenta and from your baby. The levels of these hormones, your baby's gestational age, and your age and weight are used to estimate the chance of your baby having certain chromosomal anomalies. You can have this blood test at 14-20 weeks.