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 Prenatal Genetics

​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 a woman becomes pregnant, such as a family history of a genetic condition. Others may be identified during the pregnancy through a test in the pregnancy, such as an ultrasound.

Who we Help

Who could consider a genetics consultation?

  • a woman with positive prenatal screening result (FTS, IPS, MSS)
  • a woman with abnormal ultrasound findings in a pregnancy
  • an individual with personal or family history of a known, or suspected genetic condition
  • an individual with personal or family history of a chromosome rearrangement
  • an individual with previous child with a birth defect or chromosome problem
  • an individual with questions about the risk of a genetic condition for their children

Location

Credit Valley Hospital site - room 1A100
2200 Eglinton Ave. W.
Mississauga, Ontario L5M 2N1

Hours

Monday to Friday, 8:00 am – 5:00 pm

Contact Information

Phone: 905-813-4104 Fax: 905-813-4347

Referrals

A referral from a doctor is required. For more information see What Information is Needed to Make a Referral? below. If you have any questions or wish to have one of these tests, please discuss this further with your doctor or midwife.

Resources for Patients & Their Families

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 woman.

Information About Prenatal Screening and Testing in Ontario

Why Might I Want to Consider Prenatal Screening?

It is a woman's choice whether or not she wants to have prenatal screening. You might consider prenatal screening for any of the following reasons.

Family history: People with a genetic condition, or a family history of a genetic condition, might have an increased chance of having a child with the same condition. Genetic counselling is available to review these chances and testing options.

Population Screening: Some genetic conditions, such as thalassemia and sickle cell anemia, are more common in certain parts of the world. People whose ancestors are from these areas may have an increased chance of having a child with one of these conditions. Genetic counselling is available to review testing options if a couple are both found to be carriers. See Information about hemoglobinopathies pamphlet [pdf]

Ultrasound: Ultrasound can be used to look at the developing baby for normal growth and development. Ultrasound can be done at different times in a pregnancy. It might find a baby has an increased chance of a health problem. Many times more testing would be offered. Genetic counseling is available to review these chances and testing options.

Age: All women have a chance of having a child with a chromosome difference. This chance increases slightly each year as a woman gets older. The most common condition is Down syndrome (Trisomy 21). You may wish to discuss this further with your healthcare provider.

What is Multiple Marker Screening?
Multiple marker screening provides information about the chance of having a baby with Down syndrome, trisomy 18 and an open neural tube defect. Multiple marker screening is available to all pregnant women in Ontario. There is no risk to the baby by having multiple marker screening. For more information on prenatal screening, please visit this website: http://geneticseducation.ca/public-resources/prenatal-and-preconception-genetics/guide-to-understanding-prenatal-screening-tests/

What Factors Can Affect a Prenatal Screening Result?
Accurate information about a woman’s weight, smoking status, race, whether a woman has been on insulin prior to pregnancy and whether the pregnancy was achieved by IVF, influences the accuracy of the prenatal screen result. Careful attention should be paid to ensuring this information is correct on the prenatal screening requisition.

What is NIPT (Non-Invasive Prenatal Testing)?
NIPT or Non-Invasive Prenatal Testing works by analysing the DNA fragments, of the developing baby, present in the mother’s blood during pregnancy. This is known as cell-free DNA. It is used to screen for specific chromosome anomalies including Down syndrome (trisomy 21), trisomy 18, trisomy 13 and extra or missing sex chromosomes. 
This test is a blood test that poses no risk in a pregnancy.  It can be done from 10 weeks gestation throughout pregnancy.  As a screening testing, any result that raises concerns would require verification using invasive diagnostic testing such as chorionic villus sampling (CVS) or amniocentesis.

Prenatal Diagnostic Testing
There are two common prenatal diagnostic tests available, called chorionic villus sampling (CVS) and amniocentesis. Below is a description of each test.

Chorionic Villus Sampling (CVS):
Chorionic villus sampling (CVS) is a test that looks at the chromosomes of a baby during pregnancy. It is usually done between 11 and 14 weeks of pregnancy. During the test, an obstetrician either puts a small tube through the vagina into the uterus, or puts a thin needle into the woman's belly. A piece of the placenta (chorionic villi) is taken. Testing is done on the sample. CVS can tell if a baby has Down syndrome or trisomy 18.
CVS is considered to be a safe test for both a woman and her baby. Any woman has a 4% chance of having a miscarriage at this time of pregnancy. If a woman has CVS, this chance is increased by an extra 1 out of 100 or 1%.
CVS cannot look for open neural tube defects. However, a blood test can be done at around 16 weeks of pregnancy to measure alpha-fetoprotein (AFP). This blood test can tell if there is an increased chance of a baby having an open neural tube defect. Also, an ultrasound of the developing baby done between 18 and 20 weeks of pregnancy can find many neural tube defects.
This test is not available in the Peel region. It is offered through Mt. Sinai Hospital in Toronto.

Amniocentesis:
Amniocentesis is a test that looks at the chromosomes of a baby during pregnancy. It is usually done between 16 and 22 weeks of pregnancy. During the test, an obstetrician passes a thin needle into the woman's belly and into the fluid around the baby. A small amount of fluid from around the baby is taken. Testing is then done on the fluid. Amniocentesis can tell if a baby has Down syndrome or trisomy 18.

Amniocentesis is considered to be a safe test for both a woman and her baby. Any woman has a 2-3% chance of having a miscarriage at this time of pregnancy. If a woman has amniocentesis, this chance is increased by about an extra 1 out of 200 or 0.5%.
Amniocentesis can test for open neural tube defects. This is done by measuring a protein called alpha-fetoprotein (AFP).

 

Frequently Asked Questions about Enhanced First Trimester Screening

What is Enhanced First Trimester Screening?
Enhanced First Trimester Screening (FTS) is a new first trimester screening test that uses 4 serum markers plus the nuchal translucency (NT) measurement, along with maternal age to generate a pregnancy-specific risk for Down syndrome. The two new markers that are analyzed include placental growth factor (PlGF) and first trimester alpha fetoprotein (AFP). This is in addition to PAPP-A and beta hCG, which have always been part of the FTS.
The ultrasound that is part of eFTS and eFTS-Twins usually is done between 11-14 weeks. The ultrasound looks at the size of the baby, the fetal heart beat, and measurement of the nuchal translucency (NT).

What does Enhanced First Trimester Screening screen for?
Enhanced FTS is a screening test for Down syndrome. It can also indicate when there is a high risk for Trisomy 18.

What does Enhanced First Trimester Screening not screen for?
Enhanced FTS does not screen for open neural tube defects (ONTD) or spina bifida. It does not screen for all chromosome problems in pregnancies. At this time, it is not a screening test for adverse obstetrical outcomes or pre-eclampsia, however individual practitioners may use the information from this test to identify high risk patients.

What is the recommended screen for spina bifida/ONTD?
The Society of Obstetrics & Gynecology guidelines regarding screening for fetal neural tube defects endorses the use of ultrasound (18-20 weeks) for screening of ONTD (October 2014).*

Is Enhanced First Trimester Screening a good test?
By including the two new marker​s, enhanced FTS is an improvement over FTS. It has been shown to have a detection rate that is comparable to integrated prenatal screen (IPS). We estimate a detection rate of 85-90%. See tables below.

Why should I order Enhanced First Trimester Screening for my patient?
Enhanced FTS will allow your patients to have information about their pregnancy in the first or early second trimester. For those who have a positive screen result, they can access Non-Invasive Prenatal Testing (NIPT) or diagnostic testing sooner than if they had IPS.

How do I order Enhanced First Trimester Screening?
The Trillium Health Partners (THP) Prenatal Screening Requisition has been updated and can be accessed from our website at https://trilliumhealthpartners.ca/patientservices/genetics/Pages/requisitions-forms.aspx

When can I start ordering Enhanced First Trimester Screening?
On April 3, 2017 all samples received by THP that are accompanied with a request for FTS will be reported as an enhanced FTS. After this date, the previous two marker-FTS will no longer be performed.

 

Useful Links:

Society of Obstetrics & Gynaecology of Canada: www.sogc.org
Motherisk: www.motherisk.org
Ontario newborn screening program: www.newbornscreening.on.ca