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Genetic Services

Genetic Services are only needed in some pregnancies.
 
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.

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.
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.

What are chromosomes and genes?
What is aneuploidy?
What is an open neural tube defect?
Prenatal screening tests
The genetic counselling appointment

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

What are chromosomes and genes?

The body is made up of millions of cells. Each cell contains thousands of genes, which are the instructions guiding how the body grows, develops and functions. The genes are packaged in chromosomes. We have 46 chromosomes, which come in 23 pairs. We get one copy of each chromosome from each of our parents (23 from mom and 23 from dad).

What is aneuploidy? 

Aneuploidy is when there is a difference in the number of chromosomes, i.e., an extra or missing chromosome. Down syndrome, Trisomy 18 and Trisomy 13 are all aneuploidies. These chromosome differences happen entirely by chance when a sperm or egg cell is being made. Any couple could have a baby with an aneuploidy, however the chance of this type of chromosome difference in pregnancy increases with the age of the mother.

People with Down syndrome have mental and physical challenges; some can be born with heart defects. Each person with Down syndrome is different. Prenatal testing cannot predict the level of mental delay that an individual with Down syndrome will have.

Trisomy 18 and Trisomy 13 are severe medical conditions that cause serious physical and mental disabilities. Most babies with Trisomy 18 or 13 are not alive at birth. However, some can live several months to a year. Trisomy 18 is less common than Down syndrome. It is seen in about 1 in 5,000 newborns. Trisomy 13 is rare and is seen in about 1 in 16,000 newborns.
 
 The most common aneuploidy is Downs Syndrome where the baby has an extra chromosome 21.
An aneuploidy is when the baby either has an extra chromosome or is missing a chromosome. The most common aneuploidy is Down syndrome where the baby has an extra chromosome 21.
 
Every woman, regardless of age, has a 2-3% risk of having a baby with a birth defect, such as a heart condition, cleft lip or an extra finger.
 
Aneuploidy risk goes up with the mother's age. However, you can have a birth defect without having an aneuploidy. Every woman, regardless of age, has a 2–3% risk of having a baby with a birth defect, such as a heart condition, cleft lip or an extra finger. 

Mom's age
Chance of  Down syndrome
Chance of any
chromosomal condition*
20
1/1650
1/530
25
1/1250
1/480
30
1/950
1/390
35
1/385
1/180
40
1/100
1/65
45
1/30
1/19










* Trisomy 18, Down syndrome, etc
 
Adapted from Mount Sinai Hospital's guide to prenatal screening tests Download: A guide to understanding prenatal screening tests from Mount Sinai Hospital.

What is an open neural tube defect?

Open spina bifida is an opening in the skin and bones around the spinal cord. Spina bifida can lead to physical and mental disabilities. It is difficult to predict how serious the physical problems will be and if there will be mental delays. In Ontario, about 1 out of every 2,000 babies is born with a neural tube defect. There are many factors involved in the risk for an open neural tube defect which include genetic and environmental factors. The risk for open neural tube defect does not increase with the age of the mother. Folic acid significantly reduces the risk of an open neural tube defect.

We know that taking folic acid helps to reduce the risk for an open neural tube defect in pregnancy. It is recommended to take 1 mg a day of folic acid on its own or as part of a prenatal vitamin starting  two months before conception until the second missed period.

Folic acid significantly reduces the risk of an open neural tube defect. It is important to take it starting two to three months before you get pregnant!

Prenatal screening test
 
Prenatal screening tests for Down syndrome, Trisomy 18 and open neural tube defects are available in every pregnancy. These tests tell us the chance of having a baby with one of these conditions, however they do not tell us for sure if the baby has the condition. If a screening test shows a high risk for Down syndrome, Trisomy 18 or spina bifida, then further testing, called diagnostic prenatal testing, will be offered.
Remember, screening tests can tell us if your baby has a higher than average chance of a condition - not whether it actually has it or not.
Remember, screening tests can tell us if your baby has a higher than average chance of a condition — not whether your baby actually has it or not. Most babies with the condition will be identified, but some might be missed.

Multiple marker screening tests
 
Multiple marker screening works by comparing the pattern of an ultrasound measurement and the biochemical levels in the mother's blood to the pattern we usually see in pregnancies with Down syndrome, Trisomy 18 and open neural tube defects. If the pattern matches, the risk increases. If the pattern does not match, the risk decreases.

The goal of screening is to identify most cases of Down syndrome, Trisomy 18 and open neural tube defects while keeping the number of women who need to go on to more testing as low as possible.

The goal of screening is to identify most casess of Down syndrome, Trisomy 18 and open neural tube defects while keeping the number of women who need to go on to more testing as low as possible.Multiple marker screening options include First Trimester Screening (FTS), Integrated Prenatal Screening (IPS) and Maternal Serum Quad Screening (MSS). You can speak with your health care provider about which of these options is best for you. Get more information. Download: A guide to understanding prenatal screening tests from Mount Sinai Hospital.

Non-invasive prenatal testing (NIPT)

Non-invasive prenatal testing is a new technique which measures cell-fee fetal DNA in the mother's blood. This blood test can be used to screen for Down syndrome, Trisomy 18 and Trisomy 13. NIPT can tell us of the chance is high or low for these conditions. If an NIPT test shows high risk, the woman would be offered diagnostic testing to confirm the result. NIPT has been shown to be an effective screening test in pregnant women who are 35 years of age or older and for women who have a high risk for Down syndrome or Trisomy 18 on maternal serum screening or based on an ultrasound finding. NIPT may be available more widely in the future and offer testing for other types of conditions. There is a cost for NIPT as it is only covered by OHIP in some cases.

NIPT is a screening test that can detect 98-99% pf babies with Downs Syndrome.
 
 
NIPT is a screening test that can detect 98-99% pf babies with Down syndrome. There is a less than 2% chance of the NIPT saying that the baby has Downs when in fact it doesn't. NIPT costs between $500 to $1,200 and is covered by OHIP in only certain circumstances.


I would continue my pregnancy no matter what. Should I still do these tests?
 
Speak to your caregiver about what option is right for you!
  • 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
if 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.

Chorionic Villus Sampling (CVS)

CVS is done between 12 weeks and the end of the 13th week of pregnancy. Since the placenta and the baby come from the same embryo, they have the same genetic make-up. This means we can test a piece of the placenta for chromosome abnormalities like Down syndrome. During CVS, the doctor uses a very thin tube to take a small piece of the placenta. The tube is inserted through the mother's cervix or sometimes through the mother's abdomen. CVS is associated with an increased risk for miscarriage of 1 in 100 (1%). There is about a 5% chance that the CVS result will be unclear and an amniocentesis will be needed later in the pregnancy. CVS routinely provides QFPCR and chromosome testing. CVS does not test for open spina bifida. This can be done later through a blood test at 15-18 weeks of the pregnancy and also through an ultrasound at 19-20 weeks.

Amniocentesis Amniocentesis is associated with an increased risk for miscarriage in the range of 1 in 200 (0.5%) to 1 in 400 (0.25%).

An amniocentesis is done at 16 weeks or later in a pregnancy. During amniocentesis, a needle is inserted through the mother's abdomen and a small amount of the fluid from the sac surrounding the baby is removed. Some of the developing baby's cells are floating in the fluid and these cells can be tested to tell us about the baby's chromosomes. Two tests are routinely part of amniocentesis. QFPCR counts the number of copies of the chromosomes 13, 18, 21, X and Y. QFPCR takes one to two days. A full analysis of the chromosomes is also completed; this takes about three to four weeks. Amniocentesis can detect most cases of open neural tube defects by measuring the level of a biochemical called alpha fetoprotein (AFP) in the fluid.

Amniocentesis is associated with an increased risk for miscarriage in the range of 1 in 200 (0.5%) to 1 in 400 (0.25%)

Other specialized genetic testing may be offered a CVS or amniocentesis in some cases. For instance, if a birth defect is detected on prenatal ultrasound, or if a pregnancy is known to be at risk for a specific genetic condition. If you have family members with physical or mental disabilities or a known genetic condition that you are concerned about, talk to your health care provider about a referral to the Genetics Program.

Summary of diagnostic tests

Summary of diagnostic tests chart

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

Ultrasound does not harm the mother or the baby.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.

Summary of ultrasounds

Summary of ultrasounds chart


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 We are here to answer your questions and support you, no matter what choices you make.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 at North York General is one of Ontario's largest regional genetics centres with a strong family-focused approach to patient care.
 
The Genetics program is located at North York General Hospital, 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.