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What is prenatal screening?

Prenatal screening is a non-invasive type of testing that is available to all pregnant individuals in Ontario.  Non-invasive means that there is no risk to the pregnant person or the baby.  Screening uses ultrasound, blood work or some combination of both to get information about the likelihood of a baby having a specific health condition. Screening tests do not tell you for sure if your baby has the condition, only what the chance is.
In Ontario, prenatal screening provides a pregnant person with their own chance of having a child with:
  1. Down syndrome (also called trisomy 21)
Every pregnant person starts with a chance of having a child with a chromosome difference or change (chromosomes are explained under ‘Conditions Screened’) based on their age at the time of delivery.  Screening adjusts this chance, either lowering or raising the chance based on the substances measured in the blood and/or measurements taken during the ultrasound.
No screening test screens for all chromosome abnormalities, so some may be missed.  Screening also does not screen for every birth defect.  Prenatal screening tests cannot tell you for sure whether or not your baby has one of these conditions, only the chance of it happening. To find out for sure if your baby has one of these conditions, you would have to consider a diagnostic test like chorionic villus sampling (CVS) or amniocentesis that can give you a definite answer.
Prenatal screening tests are optional – it is your choice whether to have a prenatal screening test. (Is Prenatal Screening Right for Me?)