Prenatal screening
Why Have Prenatal Screening?
Prenatal screening assesses the probability that your baby may have trisomy 21, 18, or 13. Trisomy 21, also known as Down syndrome, is one of the most common trisomies.
Anyone who is pregnant may carry a baby with a trisomy. However, the probability of trisomy 21 increases with age.
Screening estimates probability. It does not provide a diagnosis or detect every chromosomal or congenital condition.
Participation in the Québec Prenatal Screening Program is voluntary. Your physician can explain the available options and help you make an informed decision.
How to Interpret Prenatal Screening Results
A low-probability result means that your baby is unlikely to have one of the screened trisomies. However, it cannot completely rule out the condition.
A high-probability result does not confirm that your baby has a trisomy. Additional testing may be recommended, such as non-invasive prenatal testing or a diagnostic test.
Your physician will explain the appropriate next steps based on your situation.
Prenatal Screening Options
1. Québec Prenatal Screening Program
The Québec Prenatal Screening Program is available free of charge through the public health network to eligible patients. It assesses the probability that a baby may have trisomy 21, 18, or 13.
The program includes a blood test, a first-trimester ultrasound and, when indicated, non-invasive prenatal testing.
The first-trimester blood sample is taken between the 10th and 13th weeks of pregnancy, inclusively. When this period has passed, testing may be completed between the 14th and 19th weeks.
A first-trimester ultrasound is generally offered between the 11th and 13th weeks, inclusively. It helps determine gestational age and whether there is one baby or more.
Nuchal translucency may also be measured during this ultrasound. It is not available at every public facility. Fees may apply when it is performed at a private clinic.
The biochemical test is not available for twin pregnancies. Non-invasive prenatal testing may instead be offered directly.
2. Nuchal Translucency at a Private Clinic
Nuchal translucency is measured at the back of the baby’s neck during a first-trimester ultrasound.
The measurement may be combined with blood test results to provide a more accurate probability assessment. A higher measurement does not confirm that the baby has a trisomy or another medical condition.
Your physician will interpret the result based on your complete medical information. You may also review the private ultrasounds and services available at the clinic.
3. Non-Invasive Prenatal Testing
Non-invasive prenatal testing, or NIPT, analyzes fragments of placental DNA found in the pregnant patient’s blood. It screens for trisomy 21, 18, and 13.
NIPT can be performed from the 10th week of a singleton pregnancy. For a twin pregnancy, it can be performed from the 12th week.
It only requires a blood sample and does not carry a risk of miscarriage. Results are generally provided within 5 to 10 business days after the laboratory receives the sample.
In certain situations, NIPT may be offered directly through the public program. This may apply when:
- the patient will be 40 or older at the time of delivery;
- the patient is pregnant with twins;
- a previous pregnancy was affected by trisomy 21, 18, or 13;
- testing is recommended following a medical genetics consultation.
Private NIPT, such as the Harmony test available at the clinic, may also be considered.
A high-probability result must be confirmed through diagnostic testing.
Prenatal Diagnosis
Amniocentesis
Amniocentesis is a diagnostic test that can be performed from the 15th week of pregnancy.
A thin needle is inserted through the abdomen to collect a small amount of amniotic fluid. The baby’s chromosomes can then be analyzed using the cells found in the fluid.
This examination can determine with a high degree of certainty whether the baby has one of the screened trisomies. However, it carries a small risk of complications.
The risk of miscarriage is estimated at approximately 1 in 500 amniocenteses, or 0.2%. When this examination is recommended, your physician will refer you to the appropriate service and explain the procedure.
Additional Resources
Do you have questions about the available tests or the screening process? Discuss them with the healthcare professional responsible for your pregnancy care.
You may also review the steps required to schedule an appointment.