>
Calgary Sexual Health Centre Sexual Relationships button Sexual Abuse and Sexual Assault button The Body button Are You Pregnant? button Safer Sex Sexual Orientation and Gender Identity button Youth button Parent Information button Sexuality and Aging button What We Do button Training Centre button News and events button Donate Now button Side Picture © Calgary Sexual Health Centre 2009-2010. All Rights Reserved.


Pregnancy Over 35


PRENATAL TESTING
The vast majority of babies born are perfectly healthy but risks of health problems and genetic abnormalities do increase with age. If you are pregnant and over the age of 35, you can expect your physician, midwife or healthcare provider to talk with you about prenatal testing. Prenatal tests are screenings for genetic and chromosomal abnormalities including Down’s syndrome, trisomy 18 (Edward syndrome), neural tube defects (spina bifida or anencephaly), heart defects, blood disorders and abdominal wall defects.1

TO TEST OR NOT TO TEST
The decision to test or not to test is personal and depends on your family history, age, values, and potential risks. Diagnosing a problem during pregnancy can give you options for medical interventions and help you to start preparing for a child with special needs. Some people choose not to have any genetic testing because it does not matter to them what the outcome is and they don’t want to risk a miscarriage.

It is your right to decide whether to have prenatal testing or not and what tests you are comfortable with. You may chose to have no testing, some tests or all of them.

Before you undergo any prenatal testing, it is important to discuss the risks and benefits of testing with your health care provider so you are making an informed choice. We also suggest you talk with your partner and/or a trusted friend about how you feel, what you believe and what it would mean if you tested positive for a genetic or chromosomal abnormality.

The following self-questionnaire brings up some of the many issues involved in prenatal testing. There are no right or wrong answers – your answers can help you make a decision that will be right for you.

Calgary Sexual Health Centre has compiled the information contained in this article from reliable sources; however, we are not medical professionals. If you have any concerns, please contact your doctor.
SCREENING VERSUS DIAGNOSTIC TESTING
There are two categories of prenatal tests - screening tests and diagnostic tests – and it is important to understand the distinction between them.

Screening Tests
Screening tests assess the risk or chance of a specific condition being present. They do not give a definite “yes” or “no” answer; they give you a better understanding of what is likely, but not definitely, going to happen. They are not 100% accurate but can indicate if you are high risk and would benefit from further diagnostic tests. Screening tests include blood tests, ultrasounds and scans. They are non-invasive and fairly low risk to both the fetus and mother.

Prenatal screening tests include:

  • Ultrasound
  • Nuchal translucency (NT)
  • First-Trimester Screening
  • Multiple Marker Screen
  • Quad Screen
An ultrasound involves transmitting high frequency sound waves to create a picture of the uterus. Sound waves are sent through the body to create a picture of the uterus. Ultrasound scans can be used to check for an ectopic pregnancy [insert link to ectopic pregnancy in “Am I Pregnant” of Pregnancy options section], multiple pregnancies or causes of bleeding. Ultrasounds are used to examine the fetus’s organs and monitor healthy growth and development throughout the pregnancy. 2
Nuchal translucency is a special ultrasound scan that measures the collection of fluid under the skin at the back of a fetus’s neck at 10-14 weeks. If the ultrasound shows more fluid than usual, it means there is a potential risk of chromosomal abnormalities or heart defects 3. This test is by no means definitive but may prompt discussion about further testing.
A first-trimester screening involves the combination of an ultrasound and blood test to screen for Down syndrome and trisomy 18 as well as risk for heart defects. This test is done in the first trimester between 11 and 13 weeks of pregnancy and is considered a relatively accurate, non-invasive test. 4 A positive test result does not necessarily equate to an abnormality but means that further testing is worth considering.
Also called a Triple Test. The triple screen test is a blood test that looks for three specific substances - AFP, hCG and Estriol. Abnormal levels of these substances may indicate possible risk of genetic disorders. The test is done in the second trimester between the 15th and 20th week of pregnancy. It is non-invasive though it is known to have a high number of false positives 5 which may cause unnecessary stress and prompt further testing that is unwarranted.
A Quad Screen is basically the same as a triple test but includes screening for one additional substance called inhibin-A.




Diagnostic Tests
Diagnostic tests look for the presence of the specific cause of a condition. These tests take cells from the cervix, uterus or from the amniotic fluid in the uterus. Tests are not 100% accurate but are usually more accurate than screening tests. For example, the multiple marker screen is looking for conditions that are associated with Down syndrome whereas an amniocentesis is testing for the presence of an extra 21st chromosome. Diagnostic tests are more invasive and carry some risks that you need to be aware of including a slight risk of miscarriage. Ask your physician for more information about the pros and cons of diagnostic tests before you proceed.

Prenatal diagnostic tests include:

  • Amniocentesis 6
  • Chorionic Villus Sampling 8
  • Percutaneous Umbilical Blood Sampling or Cordocentesis 9
With the guidance of an ultrasound, a thin needle is inserted into the amniotic sac through the uterus and amniotic fluid is withdrawn. The amniotic sac is the fluid-filled sac surrounding the fetus to provide both protection and nutrients to the fetus. The amniotic fluid contains cells that are shed by the fetus and the sample can be analyzed to identify genetic or chromosomal abnormalities, RH-negative blood type and lung development. This test is usually done in the second trimester between the 15th to 18th weeks of pregnancy but can be performed as early as 12 weeks and as late as 20 weeks. Amniocentesis is offered to women who have had blood screens that indicate they are at higher risk for genetic problems. It is very accurate (98% - 99%) but poses a 0.5% or 1/200 chance of a miscarriage along with possible infection, cramping and bleeding. 7
A sample of the placenta tissue is withdrawn either through the cervix (most common) or the abdomen (similar to amniocentesis) and analyzed in a laboratory to identify chromosomal abnormalities and other inherited diseases such as cystic fibrosis. The main advantage of CVS over amniocentesis is that it can be performed in the first trimester between 10 and 12 weeks of pregnancy. Unlike amniocentesis, however, it does not test for neural tube defects and poses a 1% risk of miscarriage (1/200). The test is very accurate (98% - 99%) for identifying problems but it does not measure the severity of the disorders. Some women who are worried about genetic abnormalities because of their family histories will have CVS in the first trimester and follow up with amniocentesis in the second trimester if required.
With the guidance of an ultrasound, a thin needle is inserted through the uterus and into the umbilical cord and a small sample of fetal blood is withdrawn. This test is usually only performed to confirm inconclusive tests results from either an amniocentesis or chorinonic villus sampling. This test identifies chromosomal abnormalities and blood disorders but like CVS, it does not identify neural tube defects. It cannot be done until after 17 weeks of pregnancy and carries a 2% chance of Although the results can be processed in approximately 2 days, PUBS has a 2% chance of miscarriage (2/100) and may result include infection, cramping and bleedin



DOWN SYNDROME
Down syndrome is the result of an extra genetic material associated with the 21st chromosome. This extra chromosome causes limitations in physical and intellectual development. People with Down syndrome typically have physically notable characteristics: almond shaped eyes (due to epicanthal folds over the eyes), single palmar crease on the palms, flattened nose bridges and decreased muscle tone. Many people with Down syndrome are born with heart and congenital defects, many of which can be corrected with surgery. The majority of people with Down syndrome are also expected to live a normal life span. For more information, visit the Canadian Down Syndrome Society.

1 March of Dimes, (2009). Maternal blood screening for birth defects. Retrieved June 16, 2009 from http://www.marchofdimes.com/professionals/14332_1166.asp#head1
2 BabyCentre Canada, (2009). Ultrasound scans: an overview. Retrieved June 16, 2009 from http://www.babycenter.ca/pregnancy/ref/ultrasoundscansoverview/
3 BabyCentre Canada, (2009). Nuchal translucency (NT) ultrasound. Retrieved June 16, 2009 from http://www.babycenter.ca/pregnancy/antenatalhealth/scans/nuchalscan/
4 American Pregnancy Association, (February 2006). First trimester screen. Retrieved June 16, 2009 from http://www.americanpregnancy.org/prenataltesting/firstscreen.html
5 American Pregnancy Association, (February 2006). Triple test screen. Retrieved June 16, 2009 from http://www.americanpregnancy.org/prenataltesting/tripletest.html
6 BabyCentre Canada, (2009). Amniocentesis. Retrieved June 17, 2009 from http://www.babycenter.ca/pregnancy/antenatalhealth/testsandcare/amnio/#2
7 American Pregnancy Association, (February 2006). Amniocentesis. Retrieved June 17, 2009 from http://www.americanpregnancy.org/prenataltesting/amniocentesis.html
8 BabyCentre Canada, (2009). Chorionic Villus Sampling (CVS). Retrieved June 17, 2009 from http://www.babycenter.ca/pregnancy/antenatalhealth/testsandcare/cvs/
9 American Pregnancy Association, (February 2006). Cordocentesis. Retrieved June 17, 2009 from http://www.americanpregnancy.org/prenataltesting/cordocentesis.html