Genetic Services are only needed in some pregnancies. Your health care provider can make a referral if this is needed in your pregnancy. Most babies are healthy, however, about 2-3% of babies are born with a birth defect or serious medical problem.

There are many different kinds of genetic problems. Some genetic problems are caused by a change in a part of or a whole chromosome. Others are due to changes in a single gene. Some genetic problems cause only mild problems while others cause severe mental and/or physical differences. 

a mother and father hold their new baby

Prenatal tests can look for many genetic disorders in pregnancy. The most common tests look for Down syndrome, Trisomy 18, Trisomy 13 and open neural tube defects, such as spina bifida. Some women want to know ahead of time if there is a higher chance for these conditions so they can learn about all of their options and what help is available. Some women don't want to know if their baby has one of these problems until delivery. These women may choose not to have prenatal testing.

Genetic testing can tell us about the risk of major conditions, however, some conditions can be missed and not all conditions can be screened for.

Read information on prenatal screening from The Society of Obstetricians and Gynaecologists of Canada. Download: Prenatal screening 

Summary of screening tests

See our summary of screening tests document Download: Summary of screening tests

mom and baby

I would continue my pregnancy no matter what. Should I still do these tests?

  • Prenatal screening tests are entirely optional and you have a right to decline testing
  • You may still want to have testing even if it wouldn't change how you feel about the pregnancy, because if there is an abnormal result:
  • you can prepare mentally, emotionally and get extra support in place at home
  • we can prepare medically
    • for example, some babies with Down syndrome might have heart problems

    • we can have you speak to the pediatricians ahead of time so that you have all the information you need and so that the right people can attend the delivery

    • some babies with certain problems have to be delivered at Mount Sinai and not at North York General
  • sometimes screening tests will give us information about how the baby's placenta is working we know there might be a placental issue, we will follow the pregnancy more closely

Prenatal diagnostic testing

Women have prenatal diagnostic testing for a number of different reasons. Diagnostic testing may be offered to you if:

  • you will be 40 or older when the baby is born
  • you have a screen positive FTS, IPS or MSS
  • your pregnancy is known to be at risk for an inherited disease
  • an ultrasound has identified a higher risk for a problem in your pregnancy

Amniocentesis and chorionic villus sampling (CVS) are prenatal diagnostic tests. For both of these, a quick test called a QF-PCR will first look for common problems including Down syndrome. If the QF-PCR is normal, a test called a microarray is done to look for small extra or missing pieces of the baby's chromosomes. Some of these changes are known to cause birth defects or medical problems for the baby. Sometimes, we may not know the meaning of a specific change found from the microarray test and are uncertain if or how it would affect the baby. A microarray could also find changes which might not be related to the reason for testing, but may cause health problems in adults. Not all genetic diseases can be found by microarray.

Summary of diagnostic tests

TestWhat does it involve?Miscarriage riskThings to consider

CVSTaking some tissue from under the placenta with a needle under ultrasound guidance. This is done either through the abdomen or through the cervix. 1%

Can be done between 12-14 weeks.

If you want to terminate pregnancy, can do so sooner. Higher miscarriage risk. 

5% chance of an unclear result. 

Doesn't check for spina bifida (can be checked with a blood test later)

AmnioPutting a needle through the abdomen under ultrasound guidance to sample some of the water around the baby. 0.25-0.5%

Can be done 16 weeks and later. 

Lower miscarriage risk than CVS. 

Get preliminary result in 1-2 days and full analysis in 3-4 weeks. 

Can check for spina bifida at the same time. 

 

Ultrasound

Ultrasound uses sound waves to make an image of your developing baby. 

woman receiving an ultrasound

Ultrasound is used at different times in the pregnancy for different reasons. Your health care provider will arrange these ultrasounds for you. 

Early in the pregnancy, ultrasound can be useful to find out if you're pregnant and how far along in the pregnancy you are. Ultrasound can also be used to measure the nuchal translucency (NT) as part of the screening tests. The NT measures a portion of skin at the back of the baby's neck. An elevated measurement could indicate an increased risk of aneuploidy or heart defects. 


The Anatomy Scan is also referred to as the “19-20 week scan” or a “Level II” ultrasound. During this ultrasound the sonographer takes a detailed look at the developing baby from head to toe. This ultrasound can detect many physical problems or birth defects and can help to identify some chromosomal abnormalities. It is important to note that not all birth defects can be detected by ultrasound. 

Type of USWhen is it done?Things to consider

DatingUsually a 6-8 weeks if you're not sure of the date of your last period. Can help us determine when your due date is and tell us if you're having one baby or twins. 

NT11-13+6 weeksMeasures the back of your baby's neck. an abnormally thick measurement can be associated with aneuploidy or heart problems. 

Anatomy19-20 weeksA head to toe look at the baby and the placenta. This scan can detect birth defects that are not necessarily picked up by the blood tests, like cleft lip for example. However, not all birth defects can be detected. 

Your care provider may recommend further ultrasounds based on your individual needs. 

What if a problem is found?

It can be difficult to know what to do when a problem is found. Take the time to talk about all of your options with your health care provider as well as the counsellors in the genetics program. Any choice you make is up to you. You will not be pressured into making one decision or another. No matter what choice you make, we will support you.

Do I need a referral to Genetics?

Questions to ask:

  • Do I or anyone in my family have a disease that I know to be inherited?
  • Does anyone in my family have mental delay and/or physical differences?
  • Have I had three or more miscarriages or a stillbirth? Has anyone closely related to me had three or more miscarriages or a stillbirth?
  • Am I related to my spouse/partner by blood? (eg. cousins)
  • Have I taken any medication, alcohol, prescription or other drugs during my pregnancy?
  • Will I be 35 years or older when I am due to deliver my baby?

The genetic counselling appointment

The Genetics Program at North York General is one of Ontario's largest regional genetics centres with a strong family-focused approach to patient care.

At a genetics appointment, you will be seen by either a geneticist (a doctor specializing in genetics), a genetic counsellor or both. They will review your concerns and provide you with information and support to help make decisions regarding your care and the management of your pregnancy.

A geneticist or genetic counsellor will ask you questions about the health of your family members, as well as your own medical and pregnancy history to see if there are any concerns that may affect the health of the pregnancy. Testing options available to you will be described, and you may choose what you feel is best for you.

Genetic counselling is meant to provide you with information and support. The decisions you make regarding your pregnancy are entirely your own.

The Genetics program is located at North York General Hospital, 4001 Leslie Street, 3rd floor, SE wing.

 You must not rely on the information on this website as an alternative to medical advice from your doctor or other professional healthcare provider. If you have any specific questions about any medical matter you should consult your healthcare provider. If you think you may be suffering from any medical condition you should seek immediate medical attention. You should never delay seeking medical advice, disregard medical advice, or discontinue medical treatment because of information on this website.