Prenatal screening

Why a prenatal screening?

Trisomy 21, commonly referred to as Down syndrome, is the most common chromosomal abnormality in children and the first cause of intellectual deficiency. It is characterized by certain atypical physical traits, certain congenital malformations and many other health problems.

Prenatal screening assesses the impairment risk for Trisomy 21, 13 and 18; the last two being the most severe forms of Down syndrome.

Note that prenatal screening remains optional.

Various options are offered to you concerning prenatal screening. You will have the opportunity to talk it over with your doctor, in order to take the best decision for your situation.

How to interpret results from prenatal screening?

Prenatal screening allows to assess your risk of having a child with trisomy, but it is not a diagnostic. In the event that your prenatal screening indicates a low risk, there is no guarantee that your child will not be born with Trisomy. Inversely, if your result indicates a high risk, it does not necessarily mean that your baby will be born with trisomy. A diagnostic test will be necessary and your doctor will explain the steps to come.

Options of prenatal screening

1. Trisomy 21 Prenatal Screening Program of Québec

This program is offered free of charge by the government of Québec. It involves 2 blood tests: the first one between the 10th and 13th 6/7 weeks, and the second between the 14th and 16th 6/7 weeks. This program does not include an ultrasound measuring the nuchal translucency. Your doctor will recommend an ultrasound dating to determine gestational age.

Trisomy detection levels are around 85%.

2. Nuchal translucency (in a private clinic) combined with the trisomy 21 prenatal screening program of Québec

In order to increase the detection level up to 85%-90%, you can do an additional ultrasound in a private clinic. They will measure nuchal translucency and combine it with the prenatal screening program of Québec. Nuchal translucency is an ultrasound measurement of your baby's neck. It is done between 11 and 14 weeks.

3. Prenatal screening in a private clinic

Prenatest Plus

A screening test for trisomy 21 and 18. The test involves taking a blood sample and an ultrasound measurement of the nuchal translucency. It includes a foetal DNA test (Harmony) free of charge for patients having received a "high risk" result (> or = to 1/250 for trisomy 21) and "intermediate risk" (between 1/2500 and 1/251 for trisomy 21). The detection rate for trisomy 21 is >98%. The tests are done between 11 and 14 weeks.

Foetal DNA (Harmony)

There are many tests available to detect circulating cell-free foetal DNA in the mother's blood. This test poses no risk to your baby. It can be done starting from the 10th week of pregnancy. The detection rate for trisomy 21 is >99%.

*** There are several private clinics offering prenatal screening. Each of them have different prices and methods of payment.

Prenatal diagnostic


This is an invasive medical procedure for prenatal diagnosis. Amniotic fluid will be collected from a puncture through the abdomen, into the uterus. The goal is to obtain the karyotype (chromosomes) of your baby. The risk of spontaneous abortion is 1/200 to 1/400. Your doctor will refer you to the high risk pregnancy clinic (GARE) for an appointment.

You can consult the Directives for prenatal screening of trisomy 21 in Québec