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Prenatal and Newborn Screening

In March 2007, our guest experts in Le Club's Ask the Expert were Dr. June Carroll MD, CCFP, FCFP and Andrea Rideout, certified genetic counsellor.

Dr. Carroll is a family physician practicing in the Granovsky Gluskin Family Medicine Centre at Mount Sinai Hospital in Toronto. She holds the Sydney G. Frankfort Chair in Family Medicine and is an Associate Professor in the Department of Family Medicine at the University of Toronto.

Ms. Rideout is a certified genetic counsellor. She is the Project Manager for The Genetics Education Project at Mount Sinai Hospital and is a clinical counsellor at the Centre for Addiction & Mental Health in Toronto.

Dr. Carroll and Ms. Rideout are part of The Genetics Education Project, a Women’s Health Council funded project to develop and evaluate educational information about genetics and prenatal and newborn screening.

Here are their answers to your questions about Prenatal and Newborn Screening:

Q: Both my brother and sister had cystic fibrosis, and when I had my daughter we weren't able to determine if I carried the CF gene. When she chooses to have children, should she have genetic counselling? Are the genetic tests for cystic fibrosis reliable and conclusive?


A: Genetic counselling is recommended for anyone with a family history of a genetic condition, including cystic fibrosis. Our genes come in pairs. We get one copy of each of our genes from our mothers and a second copy from our fathers. Cystic fibrosis is inherited in an autosomal recessive manner. This means people who are affected with cystic fibrosis have two non-working (or disease causing) cystic fibrosis genes. Your brother and sister who had cystic fibrosis inherited one non-working cystic fibrosis gene from your mother and a second non-working cystic fibrosis gene from your father.

Since you are not affected with cystic fibrosis, two situations are possible. The first is that you inherited two working (or normal) cystic fibrosis genes from your parents.  In this situation, since you do not have a non-working cystic fibrosis gene, you cannot pass it on to your daughter. Based on your family history, your chance of having inherited two working cystic fibrosis genes from your parents is one in 3, or 33 percent. However, if your daughter’s father is a carrier of a non-working cystic fibrosis gene, she could have inherited a non-working cystic fibrosis gene from him.

The second possibility is that you inherited one working cystic fibrosis gene and one non-working cystic fibrosis gene – this means that you would not be affected with cystic fibrosis, but are a carrier of the non-working gene. Based on your family history, your risk of being a carrier of the non-working cystic fibrosis gene is two chances in three, or 67 percent.  If you do carry a non-working cystic fibrosis gene; you have a one in two chance of passing it on to your daughter. Therefore your daughter’s risk of carrying a non-working cystic fibrosis gene is approximately one chance in three, or 33 percent.

Reliable testing for cystic fibrosis is available in Ontario – it is a blood test. If you had genetic testing for cystic fibrosis in the past and no disease – causing variation was found in the cystic fibrosis gene or the results were inconclusive – then you could have updated genetic testing.

There are over 1,500 variations in the cystic fibrosis gene known to cause the condition and more are being discovered each year.  If you had genetic testing for cystic fibrosis as recent as five years ago, then you can still have updated testing.  The reason for this is that in the past most genetic laboratories only tested for the most common disease-causing variations in the cystic fibrosis gene, anywhere from three to 30 variations.  Now we have the ability to test for many more of the known variations in the cystic fibrosis gene. The first step would be to find out if your siblings had genetic testing and if any disease causing-variations were identified. If a variation was identified then you and your family can be tested for these variations in the cystic fibrosis gene.  If no variation was identified in your siblings then you can still have updated genetic testing.  If your siblings have passed away, then the laboratory may ask to do genetic testing on your parents if they are still living.

Genetic testing can take several weeks to months to complete so it is best that your family have testing for cystic fibrosis BEFORE your daughter (or other family members) decide to start a family. To arrange for genetic testing, talk to your health care provider about a referral to a genetics clinic.  For a list of genetics clinics see the Canadian Association of Genetic Counsellors’ website: www.cagc-accg.ca.

For more information about cystic fibrosis see:
March of Dimes
Genetic Home Reference
Canadian Cystic Fibrosis Foundation

 


Q: My husband and I are talking about starting a family soon.  I am 34 years old and want to know how long after I stop taking the pill can we begin trying to conceive?  As well, what kind of genetic testing should I have done considering my age, and when should I have these tests done?

A: There is no recommended wait time between stopping oral contraceptives or birth control pills and becoming pregnant. However, you should confirm this with your health care provider because there are many different types of birth control methods and the recommendations for pregnancy planning vary depending on the type of birth control that you are using.

For questions about medication, drug, alcohol or environmental exposures prior to or during pregnancy, contact Motherisk at 416-813-6780 or 1-877-327-4636 http://www.motherisk.org/women/index.jsp.

Or, see the Organization of Teratogen Information Services (OTIS) website that has fact sheets on common medication, drug, alcohol and environmental exposures during pregnancy. Fact sheets are available in English, French and Spanish. See http://www.otispregnancy.org/.

It is recommended that every woman planning to become pregnant, or who might become pregnant, take 400 micrograms (mcgs) of folic acid daily. Folic acid is a vitamin which helps to reduce the chance of having a baby with a group of birth defects involving the spinal cord and brain development known as open neural tube defects. For more information about folic acid see the March of Dimes at: http://www.marchofdimes.com/pnhec/173_769.asp.

It is your choice whether or not to have genetic screening tests during pregnancy. Every woman of any age has the choice whether or not to have prenatal genetic screening for Down syndrome, trisomy 18 and open neural tube defects. For more information about these conditions see the links below.

Down syndrome:
Genetics Home Reference: http://ghr.nlm.nih.gov/condition=downsyndrome.
March of Dimes: http://www.marchofdimes.com/pnhec/4439_1214.asp.
Canadian Down Syndrome Society:
http://www.cdss.ca/.

Trisomy 18:
Genetics Home Reference: http://ghr.nlm.nih.gov/condition=trisomy18.
March of Dimes: http://www.marchofdimes.com/pnhec/4439_1209.asp.
Support Organization For Trisomies 18, 13 and Related Disorders: http://www.trisomy.org/resources.php.

Open neural tube defects:
March of Dimes: http://www.marchofdimes.com/pnhec/4439_1224.asp.

Prenatal screening tests tell you your chance of having a baby with Down syndrome, trisomy 18 or an open neural tube defect.  Prenatal screening cannot tell for sure if your baby has one of these conditions. In Ontario there are several different prenatal screening tests. Your choice of test will depend on what is available in your area and how far along in your pregnancy you are when you see your health care provider. Prenatal screening tests are blood tests, sometimes with an ultrasound, done early in pregnancy beginning at 11 weeks or 2-1/2 months of pregnancy.

Ontario Multiple Marker Screening Program: http://www.lhsc.on.ca/programs/rmgc/mss/index.htm.
Antenatal Screening Web Resource: http://www.antenataltesting.info/.

It is also recommended that every woman have a detailed ultrasound at 18 to 20 weeks of pregnancy to see how the baby is growing and developing. For more information about ultrasound see:
March of Dimes: http://www.marchofdimes.com/pnhec/159_523.asp.

Other genetic screening tests may be appropriate if you have a family history of birth defects, developmental delay/mental retardation, inherited disease, infertility, three or more miscarriages, stillbirth, childhood deaths, consanguinity (related to your partner) or are from certain ethnic groups (Ashkenazi or Eastern European Jewish, African, Mediterranean, or Asian ancestry).  If you have a family history or any of the above conditions, talk to your health care provider about a referral to genetic services.  To locate a genetics clinic near you, see the Canadian Association of Genetic Counsellor’s website: www.cagc-accg.ca.

Ashkenazi Jewish disorders:
Hospital for Sick Children.
Canadian Association for Tay-Sachs and Allied Diseases: http://www.catsad.ca/.

African, Mediterranean, or Asian ancestry:
March of Dimes, Sickle cell disease: http://www.marchofdimes.com/pnhec/4439_1221.asp.
March of Dimes, Thalassemia: http://www.marchofdimes.com/pnhec/4439_1229.asp.

For help collecting your family history see:
The Genetic Alliance: http://www.geneticalliance.org/ws_display.asp?filter=fhh.
The US Surgeon General: http://www.hhs.gov/familyhistory/.

 



Q: I have produced five  live children and lost four babies at three months, four months, five and a half months, and two at five months. The miscarriages were not diagnosed at the babies in the 1970's.  In the 1980s University of Colorado in Denver diagnosed von Willebrand...our particular variant is difficult to manage. What is the true information about genetic screening that I may share with my four daughters and one son.  Please help us.


A: There are several different types of von Willebrand disease, and the risk for your children of inheriting the disease depends on which type you have. All of your first degree relatives (parents, brothers, sisters, children) should see a hematologist (a doctor specializing in blood diseases) to determine if they have von Willebrand disease.

For any female relatives that have this disease, there are special care recommendations during pregnancy which they should discuss with their health care provider.  There is genetic testing available for von Willebrand disease.  If you are interested in learning more about von Willebrand disease and risks to your family members, talk to your health care provider about a referral to genetic counselling. If you are located in Canada, the Canadian Association of Genetic Counsellors’ website for a genetics clinic near you is: www.cagc-accg.ca or if you are in the United States, please see the National Society of Genetic Counsellors’ website for a genetics clinic near you: www.nsgc.org.

The same prenatal genetic screening tests for Down syndrome, trisomy 18 and open neural tube defects are also available to you and your family. See the answer to Question 2.

For more information about von Willebrand disease see:
http://www.noah-health.org/en/blood/hemophilia/types/vonwillebrand.html.

 


Q: I know this is a big question, but what are the pros and cons of prenatal and newborn screening? How should I educate myself so I can make the right decisions?

A: Part 1: Prenatal Screening

Things to consider when deciding about prenatal screening for Down syndrome, trisomy 18 and open neural tube defects:

ADVANTAGES:

  • Prenatal screening tests provide information about the health of your baby.
  • Test results may be reassuring.

DISADVANTAGES:

  • Waiting for prenatal screening test results may be stressful.
  • Test results may cause you to worry about the health of your baby or become depressed.
  • Screening tests do not find every kind of condition.

Some questions about prenatal screening to ask yourself and perhaps discuss with your partner:

  1. Do you want to know the chance of your baby having Down syndrome, trisomy 18 or open neural tube defect?
  2. If your result shows the chance is higher than expected (called SCREEN POSITIVE), you will need to decide if you want more testing to find out for sure if your baby has Down syndrome, trisomy 18 or open neural tube defect.
  3. More testing, as such as amniocentesis and CVS can tell for sure if your baby has Down syndrome or trisomy 18 and has a small chance of miscarriage. How will you deal with this?  For more information about amniocentesis and CVS see other questions in this series.
  4. If more testing shows your baby has a condition for sure, what will you do with the information? You will need to decide if you want to continue or end the pregnancy.
  5. How will this information affect your feelings throughout the rest of your pregnancy?
  6. If you have a child with mental and/or physical disabilities, how will this affect your life, your other children, your relationship with your partner and your family?

Part 2 Newborn screening

ADVANTAGES

  • Newborn screening tests provide information about the health of your baby
  • Test results may be reassuring
  • If your baby is affected with a condition on the newborn screening panel, then early treatment in some but not all cases may save your child’s life and/or improve the health and development of your child.
  • Information about conditions that run in your family can help with family planning decisions.

DISADVANTAGES

  • Waiting for newborn screening test results may be stressful.
  • Test results may cause you to worry about the health of your baby or become depressed.
  • Screening tests do not find every kind of condition and in rare cases can miss a baby affected with a condition on the newborn screening panel
  • Unanticipated outcomes – sometimes during the test process, non-paternity can be revealed.
  • Labelling – in some cases a baby may be identified as having a mild condition that does not require treatment as a result of newborn screening.

Remember: Screening tests will identify most babies with Down syndrome, trisomy 18 or open neural tube defect or a condition on the newborn screening panel. However, screening tests will not identify every baby with these conditions.

 


Q: I have heard that newborn screening is just coming in Ontario. What disorders are being screened? Is it optional? If so, why?

A: Ontario is in the process of expanding its newborn screening program from two to over 28 conditions by the end of 2007. Newborn screening is done with a heel prick blood sample taken when the baby is between 24 and 72 hours of age. The conditions screened for are very rare, but can cause serious problems if not detected and treated early. Often treatment consists of a special diet. It is your choice whether or not to have newborn screening, but remember that this screening finds babies with these conditions early, usually before mental or physical problems have occurred and usually early enough that treatment can make a difference.

The conditions that will be on the Ontario newborn screening panel by the end of 2007 are:

20 inborn errors of metabolism which include:

Nine organic acid disorders: in these conditions, the body cannot metabolize certain amino acids and fats leading to the accumulation of organic acids in blood and urine which causes serious potentially preventable effects on health and development, including death.

  • Isovaleric acidemia  (IVA)
  • Glutaric acidemia type 1 (GA1)
  • Hydrodroxymethylglutaric acidemia (HMG)
  • Multiple carboxylase deficiency (MCD)
  • Methylmalonic acidemia (MUT)
  • Methylmalonic acidemia (Cbl A, B)
  • 3-methylcrotonyl glycinuria (3MCG)
  • Propionic acidemia (PROP)
  • Β-ketothiolase deficiency (BKT)

Six fatty acid oxidation disorders: in these conditions the body cannot break down fatty acids which are an essential part of the body’s ability to produce energy. Fatty acid disorders can be a cause of sudden infant death syndrome (SIDS).

  • Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency
  • Very long-chain acyl-CoA dehydrogenase deficiency (VLCAD)
  • Long-chain L-3-OH acyl-CoA dehydrogenase deficiency (LCHAD)
  • Trifunctional protein deficiency (TFP)
  • Carnitine uptake defect (CUD)

Six amino acid disorders: these conditions occur when the body cannot either metabolize or produce certain amino acids, resulting in toxic accumulation which can cause serious potentially preventable effects on health and development, including death.

  • Phenylketonuria (PKU)
  • Maple syrup urine disease (MSUD)
  • Tyrosinemia type 1 (TYR 1)
  • Homocystinuria (HCY)
  • Citrullinemia (CIT)
  • Argininosuccinic aciduria (ASA)

Three hemoglobinopathies: in these conditions, there is a change in the shape of or the amount of the haemoglobin molecule in blood which interferes with the ability to carry oxygen to the brain and other tissues.

  • Sickle cell disease (Hb SS)
  • Hemoglobin SC disease
  • Sickle-β thalassemia (Hb S/β-thal)
  • Other hemoglobin variants may be picked up

Two endocrine disorders: in these conditions, the body does not produce enough of the necessary hormone(s) needed for growth or normal sexual and mental development.

  • Congenital hypothyroidism (CH)
  • Congenital adrenal hypoplasia (CAH)

Three other disorders:
Galactosemia (GALT) – disorder of sugar metabolism
Biotinidase deficiency (BIOT) – lack of vitamins necessary for normal metabolism
Cystic fibrosis (CF) – lung disease

Some provinces (such as Ontario) also offer screening for hearing.

For more information about Ontario’s newborn screening program see the Ontario Ministry of Health and Long Term Care’s website: http://www.health.gov.on.ca/

March of Dimes: http://www.marchofdimes.com/pnhec/298_834.asp

National Newborn Screening & Genetics Resource Center: http://genes-r-us.uthscsa.edu/

If you live in a province that does not offer expanded newborn screening and you are interested in obtaining expanded newborn screening for your baby see:
http://genes-r-us.uthscsa.edu/resources/newborn/commercial.htm

 



Q:
Can you give me any ideas on how to persuade family members to get their newborns screened? I am at a loss to understand why my cousins who get pregnant don’t want to get screened even when they have my child as an example of someone who could be dead by now if she hadn’t been screened.

A: The decision to have prenatal screening and newborn screening is very personal and some people want to keep their decisions private. See above questions for some of the advantages and disadvantages of newborn screening.

 


Q: My five-year-old son has classic galactosemia that was found by newborn screening. I know that the dangers of developmental disabilities, liver failure, blindness and other potential problems can be reduced by newborn screening and avoidance of foods containing galactose. But recently I came across a 1994 research report that said there was a sudden decline in intelligence after age six, even when the condition is well managed by the right diet. My husband and I are wondering why we never hear about this when we read about galactosemia on consumer websites. Could you comment please?


A: Generally, for most but not all metabolic conditions, dietary and medical management will improve an affected child’s health and development.  However, these treatments are not a cure for many metabolic diseases and children may still experience a variety of health and developmental issues. Our suggestion would be to contact a geneticist who specializes in metabolic conditions like galactosemia and ask for a consultation to obtain updated genetic counselling/information about galactosemia.

There are several genetic centres in Ontario that specialize in metabolic conditions such as the Hospital for Sick Children in Toronto and the Children’s Hospital of Eastern Ontario in Ottawa. To find a genetics centre near you, see the Canadian Association of Genetic Counsellors’ website: www.cagc-accg.ca.

 



Q:
What are the differences between Amniocentesis and CVS? That was confusing for us the first time we were pregnant. We’d like to be better prepared to make the right decision the second time.


A: Prenatal screening tests give you your chance of having a baby with Down syndrome, trisomy 18 and open neural tube defects.  Screening tests cannot tell you for sure if your baby has one of these conditions. However, diagnostic tests such as amniocentesis and CVS can tell for sure if your baby has one of these conditions. These tests are available only if your screening test result for Down syndrome, trisomy 18 or open neural tube defects is screen positive (an increased risk of having a baby with one of  these conditions) or if you are 35 years of age or older and in certain other situations.

Chorionic Villus Sampling (CVS):
CVS is a test that can tell for sure if your baby has Down syndrome or trisomy 18. This test is done between 11 and 14 weeks of pregnancy. With CVS testing, a sample of tissue is obtained from the placenta.  This tissue can be tested for a variety of genetic conditions including Down syndrome. CVS is usually performed by inserting a tube in the vagina and using gentle suction to obtain a small piece of tissue. Any woman can have a miscarriage at this time of pregnancy. If she has CVS, this risk is increased by an extra one in 100 (1 percent). The result is available in 2-3 weeks. For more details, discuss CVS with your health care provider. CVS is not available in all areas. For more information about CVS see:
March of Dimes http://www.marchofdimes.com/pnhec/159_521.asp.

Amniocentesis:
Amniocentesis can tell for sure if your baby has a condition like Down syndrome or trisomy 18. The test is usually done between 15 and 20 weeks of pregnancy. With amniocentesis, a sample of amniotic fluid (water around the baby) is obtained through a thin needle inserted through the mother’s abdomen. The fluid contains the baby’s skin cells that can be tested for a variety of genetic conditions including Down syndrome. Any woman can have a miscarriage at this time of pregnancy, but, if she has amniocentesis, this risk is increased an extra 0.5 in 100 or 1 in 200 (~0.5 percent). The results are available in 2-3 weeks. For more details, please talk to your health care provider. For more information about amniocentesis see:
March of Dimes: http://www.marchofdimes.com/pnhec/159_520.asp.

Most times, amniocentesis or CVS will show that your baby does not have Down syndrome, trisomy 18 or open neural tube defect but these tests cannot find every condition.  Remember that most babies are born healthy. If you have more questions about amniocentesis or CVS please talk to your health care provider or ask for a referral to a genetic counsellor. To find a genetics centre near you, see the Canadian Association of Genetic Counsellors’ website: www.cagc-accg.ca.

 



Q: My grandson has an inherited metabolic disorder. Is there any way I can get tested to see whether it comes from my side of the family or my deceased husband’s side? If I knew, then family members would know better whether they should get newborn testing or not. I live in Ontario.


A: Genetic testing is available for most inherited metabolic disorders but not all.  The first step is to see if your grandson has had genetic testing.  If your grandson has had genetic testing then you and other family members can be tested.  If your grandson has not had genetic testing then he must go to a genetics centre to arrange testing. If genetic testing is not available for your grandson’s condition, then family members may be able to find out if they are carriers of the metabolic condition by other means – usually blood tests.  These other tests can be arranged through your local genetics centre. To find a genetics centre near you see the Canadian Association of Genetic Counsellors’ website: www.cagc-accg.ca.

 



Q: Our first child has a metabolic genetic disorder that was found by newborn screening. If we have a second child, should we store the cord blood in a hope that the stem cells within can help with a treatment for our first child's disorder?


A: Umbilical cord blood storage may be a good idea for your family.  Some inherited metabolic conditions can be treated with stem cells from umbilical cord blood. However most of the inherited metabolic diseases that are currently treatable with stem cell therapy are not on the newborn screening panel. Researchers are working on improving treatment of inherited metabolic diseases. There is a possibility that in the future a stem cell therapy may be available for your child’s condition. To find out if there are ongoing research studies about stem cells or other new therapies for your child’s condition – talk to your health care provider.

 



Q: Are there any specific types of prenatal screening tests, relative to age, that are recommended for women over the age of 35 as compared to a woman who is less than 35 years of age?  E.g. to rule out possible/potential risks for congenital anomalies?


A: As women get older, they have a higher chance of having a baby with a chromosome disorder like Down syndrome. No matter what age a woman is, the most likely outcome of pregnancy is a healthy baby.  At 25, the chance of having a baby with Down syndrome is 1 in 1,250, at 30 it is 1 in 950, at 35, it is 1 in 385 and at 40 it is 1 in 100.  For more information about chromosome disorders see:
March of Dimes: http://www.marchofdimes.com/pnhec/4439_1209.asp.

Screening with blood tests, or blood tests plus an ultrasound, gives you information about your personal chance of having a baby with Down syndrome or trisomy 18. This personal information is more accurate than the chance due to your age alone. Women who are going to be 35 years or older at their due date are also offered other tests such as amniocentesis and chorionic villus sampling (CVS).  Amniocentesis and CVS can tell you for certain if your baby has a chromosome disorder like Down syndrome or trisomy 18. You could decide not to have prenatal screening and have CVS or amniocentesis instead. Remember that CVS and amniocentesis have an increased chance of miscarriage.

Women who have strong family histories or risk factors for hereditary conditions or birth defects or whose prenatal screening blood test results show an increased chance of having a baby with Down syndrome or trisomy 18 can also have amniocentesis or CVS.

 



Q: What are the steps for prenatal screening? How effective are they? I am 35 and just took an IPS#1 for my first pregnancy I am in my 15th week and will be getting my IPS#2 in week 19. I know we are looking at spinal cord formation and fluid at the base of the scull for Down syndrome but what other tests can do they do? What are the percentages of false positives?


A: The steps in prenatal screening depend on which prenatal screening test you choose.  IPS or Integrated Prenatal Screening is a two step test. There are two different IPS tests, the first is just ‘IPS’ and the second is Serum IPS. The first step in IPS is a nuchal translucency ultrasound and a blood test performed at 11 to 13 weeks of pregnancy.  The first step in Serum IPS is just a blood test at 11 to 13 weeks of pregnancy. The second step is the same for IPS and Serum IPS which is a blood test at 15 to 20 weeks of pregnancy.  The other prenatal screening tests for Down syndrome are listed below.  Detection rate is a measurement of how good the test is at finding babies who have Down syndrome.

TEST

WHEN/HOW IS THIS TEST DONE?

DETECTION RATE (ACCURACY)

FALSE POSITIVE RATE**

Integrated Prenatal Screening(IPS)

At 11-13 weeks:
•1st blood test
•Nuchal translucency ultrasound*
Then at 15-20 weeks:
• 2nd blood test
No result until after the 2nd blood test

Of every 100 pregnancies with Down syndrome, about 90 will be detected. (85 - 90 percent)

About 2 out of 100 pregnancies(2 - 4 percent)

Serum Integrated Prenatal Screening (SIPS)

At 11-13 weeks:
•1st blood test
Then at 15-20 weeks:
•2nd blood test
No result until after the 2nd blood test

Of every 100 pregnancies with Down syndrome, about 85 will be detected. (80 - 90 percent)

About 2 out of 100 pregnancies.

(2 - 7 percent)

First Trimester Screening(FTS)

At 11-13 weeks:
•1st blood test
•Nuchal translucency ultrasound*
Earlier result

Of every 100 pregnancies with Down syndrome, about 80 will be detected. (80 percent)

About 3 out of 100 pregnancies(3 - 9 percent)

Quadruple Maternal Serum Screening (Quad Screening)* In many areas Quad screening has replaced by Triple screening.

At 15-20 weeks:
•blood test

Of every 100 pregnancies with Down syndrome, about 75 will be detected. (75 percent)

About 5 out of 100 pregnancies.
(5 - 7 percent)

Triple Maternal Serum Screening (Triple Screening)

At 15-20 weeks:
•blood test

Of every 100 pregnancies with Down syndrome, about 70 will be detected. (70 percent)

About 7 out of 100 pregnancies
(7 percent)

 

*Nuchal Translucency (NT) is a fluid-filled space at the back of every baby’s neck. An ultrasound to measure this is done between 11 and 13 weeks of pregnancy. The chance of a condition, like Down syndrome, is higher when the NT measurement is larger than expected.

**What is a False Positive Result?

Every screening test will produce some false positive results, for example out of every 100 women having Integrated Prenatal Screening between 2 and 4 women will have a screen positive result.  More tests like amniocentesis or CVS will show the baby does not have Down syndrome most of the time.  The positive screening result is false when more testing or the baby’s birth confirms the baby does not have Down syndrome or trisomy 18.

For more information about prenatal screening tests see:

Ontario Multiple Marker Screening Program: http://www.lhsc.on.ca/programs/rmgc/mss/index.htm

Antenatal Screening Web Resource: http://www.antenataltesting.info/

 

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