Prenatal screening
Why a prenatal screening?
Trisomy 21, commonly known as Down syndrome, is the most common chromosomal abnormality in children is often associated with. People with Down syndrome often have certain characteristic traits some congenital malformations and several other health problems. However, only 1/3 babies with trisomy 21 will have physicale malformations that can be detected on ultrasound. This therefore means that the majority of cases will go undetetected. Advanced maternal age is risk factor for trosomy 21 but it is not the only one. That's why we offer prenatal screening to each of our patients.
Prenatal screening assesses the risk of a patient carryin a baby affected by trisomy 21, 13 and 18; the latter two being the most severe forms of trisomy. It is importaant to note that there is no prenatal test that can detedt all possible birth defects.
For more information on prenatal screening, wu suggest that you consult the Qubec Government's web
Note that prenatal screening remains optional.
Different options are available to you regarding prenatal screening. You will have the opportunity to discuss it over with doctor during your first pregnacy visit, to make the best decision for you.
How to interpret results from prenatal screening?
Prenatal screening assesses your risk of having a child with trisomy, but it is not a diagnosis. In the event that the result prenatal screening is of a low risk, this cannot guarantee that your child will not have trisomy. Conversely, if the result indicates a high probality, it does not necessarily mean that your baby will be affected. If your screening test comes back as a high risk of trisomy a diagnostic test will then be necessary and your doctor will explain proceed.
Prenatal screening options
1. Quebec Prenatal Screening Program (PQDT21)
This program is offered free of charge by the government of Quebec to patient who hold a valid RAMQ card. . It includes 1 blood test: between 10th and 13th 6/7 weeks. For pregnant patients who have exceeded the first trimester and wish to be screened, a blood test of the second trimester 14-203/7 weeks can be carried out. The program does not include an ultrasound to measure nuchal transucency. A dating ultrasound should be performed to ensure the test is as accurate as possible. measuring the nuchal translucency. Your doctor will recommend an ultrasound dating to determine gestational age.
The detection rate of trisomy 21 with PQDT21 is about 85-95%.
2. Nuchal translucency (private clinic) combined with the Québec prenatal screening program (PQDT21)
To increase the detection rate between 85-90%, you can do an additional ultrasound in a private clinic to measure nuchal translucency and combine it with the Quebec prenatal screening program. Nuchal translucency is an ultrasound measurement of your baby's neck. It is done between 12 and 13 4/7 weeks. An increase in the mesurement of nuchal translucency may also mean that the baby may be affected by a disease other than trosomy, such as Noonan symdrome, a cardiac abnormality or an increased risk of miscarriage.
3. Prenatal screening in a private clinic
Foetal DNA (Harmony)
There are several tests to detect fetal DNA in maternal blood. This test does not involve any risk for your babay. It can be done as early as the 10th week. The detection rate for trsomy 21 is >99%. The results are generally available after 7-10 business days. It should be noted that in recent years, the Government of Quebec has been offering the foetal dna tes free of charge to patients who meet specific criteria, such as maternal age over 40 years of age ar delivery, twin pregnancies or history of pregnacy affecte by trisomy. The fetal sex can also be known by fetal DNA. It is recommended to combine fetal DNA with the ultrasound measurement of nuchal translucency or, at least, with a dating ultrasound.
Prenatal diagnostic
Amniocentesis
This is an invasive medical procedure for prenatal diagnosis that can be performed after the 15th week of pregnancy in certain specific cases. Amniotic fluid is collected by needle through the abdomen, and through the uterus in order to obtain your baby's karyotype(chromosones). The risk of spontaneous abortion is estimated between 1/200 to 1/400. Your doctor will refer you to the high risk pregnancy clinic (GARE) for an appointment, should it be required.
You can consult the Quebec Prenatal Screening Guideline for Down syndrome for a checklist of how to proceed.
For more information on prenatal screening, we suggest that you consult the Quebec Government's website at:
https://www.quebec.ca/sante/conseils-et-prevention/depistage-et-offre-de-tests-de-porteur/programme-quebecois-de-depistage-prenatal or talk tu your doctor about it at your next appointment.