• Prenatal screening is a way for you to determine the chance your baby may or may not have trisomy 21 (Down syndrome) or trisomy 18. Anyone may have a pregnancy with trisomy 21 or trisomy 18, regardless of their family history. This chance increases with the age of the mother (or the age of egg donor).

• Sometimes prenatal screening can tell you about the chance for other genetic conditions, such as trisomy 13 and sex chromosome differences. The current guidelines in Ontario  do NOT currently support screening for a group of conditions called microdeletion syndromes, such as 22q11.2 deletion syndrome.

• Prenatal screening poses no risk to the pregnancy as it involves ultrasound and blood work.

• Prenatal screening is not diagnostic.  Only diagnostic testing, such as chorionic villus sampling or amniocentesis, can give you a “yes” or “no” answer about trisomy 21 and trisomy 18 during the pregnancy.

• Prenatal screening is available to all pregnant individuals in Ontario, and can be ordered through your health care provider. The routine pregnancy care you receive from your health care provider will not be affected whether or not you choose to have this screening.

Types of Prenatal Screening

Multiple Marker Screening 

Traditional prenatal screening is funded by the Ministry of Health for all pregnant individuals in Ontario. How far along you are in the pregnancy, how many babies you are carrying, and availability in your area will determine which of these two tests is possible for you:

• enhanced first trimester screening (eFTS), which includes the nuchal translucency (NT) ultrasound

• maternal serum screening (MSS)

Non-invasive Prenatal Testing 

Non-invasive prenatal testing (NIPT) is a highly effective screen and it is funded by the Ministry of Health in certain situations. NIPT can be paid for out-of-pocket (self-pay) by those who do not meet any of the funding criteria. 

Notes

1. The detection rate and false positive rate for the screening tests were obtained from Ontario data. A more in-depth look at the data is available in the provider tools section.
2. eFTS may be less available during the COVID-19 pandemic. In response to this, a temporary change has been made to MSS screening cut-off to make trisomy 21 detection rate similar to that of eFTS.

Deciding if Prenatal Screening is Right for You

No one can tell you if prenatal screening is right for you. It is a personal decision and there is no right or wrong answer. All prenatal screening is optional. You might ask yourself:

• How important is it for you to know if there is an increased chance of a chromosome difference that could affect your baby's health and development?
• If your screen result is positive, how likely are you to consider more testing?
• How useful would it be for you to know about a chromosome difference before your baby's birth to prepare? When there is a chromosome difference, the health care provider may recommend changes to how the pregnancy is looked after, or the birth plan. You may wish to discuss the decision with your health care provider if you have further questions.
• What are your thoughts about continuing or ending your pregnancy if your baby has a chromosome difference?
• How would knowing or not knowing affect you emotionally throughout the pregnancy?

If you decide that you don't want to have these tests, your health care provider will continue to provide you with care. You can still consider having ultrasounds in your pregnancy which offer valuable information about the pregnancy, beyond screening for trisomy 21 and trisomy 18. These ultrasounds will give you information such as:

• how far along your pregnancy is;
• how many babies you are carrying; and
• whether there are concerns with the baby's growth and anatomy.

Referral for Genetic Counselling

If you did not have prenatal screening, if your genetic prenatal screening results are not reassuring, or you have other concerns, you may consider talking to your health care provider about being referred to the nearest genetics centre.