Prenatal genetics includes genetic counselling and testing for a variety of conditions which can be found for a developing baby during a pregnancy. This can include inherited and non-inherited conditions. Some conditions can occur in a baby regardless of medical history while others can be passed down in a family.
Most babies are born healthy. Some babies have an increased chance of having a genetic condition. Some of these concerns are identified before pregnancy, such as family history of a genetic condition. Others may be identified during the pregnancy through a test in the pregnancy.
- SERVICE UPDATE: There have been changes to our prenatal screening services:
Who we Help
Any pregnant individual with:
- a positive prenatal screening result meeting certain criteria
- a high risk, inconclusive or a failed Non-Invasive Prenatal Test (NIPT) result
- an abnormal ultrasound finding in pregnancy
- a personal or family history of a chromosome rearrangement
- a personal or family history of a birth defect or chromosome problem
- questions about the risk of a genetic condition for their children
Credit Valley Hospital site - room 1A100
2200 Eglinton Ave. W.
Mississauga, Ontario L5M 2N1
Monday to Friday, 8:00 am – 5:00 pm
Phone: 905-813-4104 Fax: 905-813-4347
A referral from a doctor is required. For more information see What Information is Needed to Make a Referral? below.
What Information is Needed to Make a Referral?
Helpful information to give to your healthcare provider:
- Relevant family history including:
- who in the family has the condition(s)
- how are they related to you
- age of diagnosis
- Medical records for the affected individual such as:
- genetic test results
- doctor’s consultation letters
- pathology reports from surgery
- test results, such as x-rays, ultrasounds, blood work
What Should I Expect During a Genetic Counselling Appointment?
You will meet with a genetic counsellor or geneticist, or sometimes both. During the appointment a family history will be taken. The genetic counsellor or geneticist will discuss the reason for referral and explain the results of any testing that was done before to the appointment. The testing options available will be discussed which might include: ultrasound, prenatal screening, prenatal testing, and genetic testing.
The genetics team is dedicated to working with women to help them understand complex information about some tests available in a pregnancy to look at the health of the developing baby. The choice to have testing is always up to the pregnant individual.
Information About Prenatal Screening and Testing in Ontario
It is a pregnant individual’s choice whether or not to have prenatal screening. For more information on prenatal screening and testing, please visit the Prenatal Screening Ontario website at https://www.prenatalscreeningontario.ca/en/pso/index.aspx. Below is a brief summary of options.
What is Prenatal Screening?
Prenatal screening are tests that can tell you what the chances are that your baby may have trisomy 21 (Down syndrome) or trisomy 18. Prenatal screening poses no risk to the pregnancy as it involves ultrasound and/or blood work.
Prenatal screening is not diagnostic. If you receive a screen positive prenatal screening result, further testing by a diagnostic testing, such as chorionic villus sampling or amniocentesis, would need to be done to confirm if your baby truly has Down syndrome or another chromosome difference.
Prenatal screening is available to all pregnant individuals in Ontario and can be ordered through your health care provider.
Types of Prenatal Screening Tests
There are two types of prenatal screening tests, Multiple Marker Screening and Non-Invasive Prenatal Testing (NIPT).
Multiple Marker Screening (MMS)
Multiple Marker Screening (MMS) is funded by the Ministry of Health for all pregnant individuals in Ontario. How far along you are in the pregnancy and other factors will determine which of these two tests is available to you.
Enhanced first trimester screening (eFTS)
eFTS involves a nuchal translucency (NT) ultrasound and a blood sample. eFTS can be done between 11+3 weeks and 13+6 weeks of pregnancy.
Maternal serum screening (MSS)
MSS involves only a blood sample. MSS can be done between 14+0 and 20+6 weeks of pregnancy. MSS is usually done if the window for eFTS was missed or if an NT ultrasound is not accessible.
Non-Invasive Prenatal Testing (NIPT)
NIPT uses placental DNA circulating in the pregnant individual’s blood to screen for trisomy 21, trisomy 18 and trisomy 13. It also can screen for sex chromosome abnormalities. NIPT is only funded by the Ministry of Health if a pregnant individual meets certain criteria. Otherwise, a patient has the choice to self-pay for NIPT should they wish.
While NIPT is more effective that eFTS and MSS, it is still a screening test. This means that further testing, either by chorionic villus sampling or amniocentesis, is needed to confirm a high risk NIPT result.
What is Diagnostic Prenatal Testing?
Diagnostic prenatal tests are tests that can determine if a baby truly has trisomy 21, trisomy 18, trisomy 13 and sex chromosome abnormalities. Diagnostic prenatal tests are only available to pregnant individuals who meet certain criteria. These tests pose a small risk of miscarriage for the pregnancy. These tests are usually ordered by specialists.
There are two types of diagnostic prenatal tests, chorionic villus sampling (CVS) and amniocentesis.
Chorionic Villus Sampling (CVS)
Chorionic villus sampling (CVS) is usually done between 11 and 13 weeks in pregnancy. During the test, an obstetrician either inserts a small tube through the vagina into the uterus, or inserts a thin needle into the pregnant individual’s belly. A piece of the placenta (chorionic villi) is taken.
CVS is considered to be a safe test for both the pregnant individual and the baby. Any pregnant individual has a 4% chance of having a miscarriage at this time of pregnancy. If CVS is done, this chance is increased by an extra 1 out of 100 or 1%.
Amniocentesis is usually done between 16 and 22 weeks in pregnancy. During the test, an obstetrician passes a thin needle into the pregnant individual’s belly and into the fluid around the baby. A small amount of the fluid around the baby is removed.
Amniocentesis is considered to be a safe test for both the pregnant individual and the baby. Any pregnant individual has a 2-3% chance of having a miscarriage at this time of pregnancy. If amniocentesis is done, this chance is increased by an extra 1 out of 200 or 0.5%.
Prenatal Screening Ontario: https://www.prenatalscreeningontario.ca/en/pso/index.aspx
Society of Obstetrics & Gynaecology of Canada: www.sogc.org
Ontario newborn screening program: www.newbornscreening.on.ca