Screening Tests

Screening Tests for You & Your baby


Early in the pregnancy you will be offered a number of tests. The purpose of these tests is to check whether you have any conditions or infections that could affect your or your baby’s health. You do not have to have a particular test if you do not want it, however, the information these tests can provide may help us provide the best care possible during your pregnancy and birth. The test results may also help you to make choices during pregnancy. It is important to let us know if you think you have been exposed to any infection. Further information on many of these tests can be found in ‘Babies Best Chance.’


NOTE: HIV, Syphilis, Chlamydia, Gonorrhoea, Herpes, Hepatitis & Rubella are all reportable diseases in BC which means that if you have a positive result, the laboratory automatically informs the Public Health office so they can track and record the treatment of these conditions.


Early Pregnancy – tests for the mother


We offer screening tests for;

  1. Anaemia
  2. Blood group and Rhesus (Rh) status
  3. Rubella immunity
  4. Hep B
  5. “Overt” or pre-existing diabetes (if risk factors present)
  6. Asymptomatic bacteriuria
  7. HIV
  8. Syphilis
  9. Chlamydia
  10. Gonorrhoea
  11. Herpes simplex
  12. Cervical pap smear


Additional screening tests we may offer (depending on individual case history);

  1. Ferritin and B12
  2. Hep C
  3. Toxoplasmosis
  4. Chickenpox (and chickenpox immunity)
  5. Bacterial vaginosis/Yeast infection
  6. Parvovirus (and parvovirus immunity)


What is Maternal Serum Screening?


The Maternal Serum Screen (MSS) is an optional blood test that is available to all pregnant women in British Columbia. This test, which poses no risk to the pregnancy, estimates a woman’s chance of having a baby with Down syndrome (Trisomy 21), Open Neural Tube Defects (e.g., Spina Bifida) and Edwards syndrome (Trisomy 18). It is very important to understand that this screening test is NOT a diagnostic test; it can only indicate if a pregnancy is at a greater or lesser risk of the above conditions. Women who are found to be at increased risk are offered further diagnostic testing such as detailed ultrasound examination and/or amniocentesis.


Not all affected pregnancies are detected by the MSS. The screen can detect approximately 79% of cases of Down syndrome, 85% of Open spina bifida and 60% of Trisomy 18.


How and when is the test done?

The MSS is two blood tests that can ONLY be done at specific times in pregnancy: the first between 10 and 14 weeks of pregnancy, and the second between 15 and 21 weeks of pregnancy. If you have missed the first blood test, you can still do the second, but the results will not be as accurate. The test measures the levels of several proteins in your blood, such as PAPP-A, alpha-fetoprotein (AFP), unconjugated estriol (uE3), and human chorionic gonadotropin (hCG). These are made by the baby or the placenta, and are measured in the expectant mothers blood. The levels of these proteins are different in some pregnancies affected with Down syndrome, neural tube defects, or Trisomy 18. These protein levels in combination with maternal age, weight, and other factors are used to estimate the risk in each pregnancy.


What is a Nuchal Translucency Ultrasound?

A nuchal translucency ultrasound provides a measurement of the skin on the back of the fetus’s neck. This measurement, when combined with the blood test results, lowers the false positive rate of the test. This measurement must be taken between 10 and 14 weeks of pregnancy. Nuchal translucency ultrasounds are covered by MSP for the following women:

  1. Women ≥ 35 year old at expected date of delivery (EDD);
  2. Women with twin pregnancies;
  3. Women who have a history of a previous child or fetus with Down syndrome, trisomy 18 or trisomy 13;
  4. Women who are HIV positive; and
  5. Women pregnant following in vitro fertilization with intracytoplasmic sperm injection (IVF with ICSI) Women who are not covered by MSP for a nuchal translucency ultrasound may choose to pay to have one done. Visit the Early Pregnancy Assessment Unit’s website for more information about this option:, or ask your midwife for more information.


What does a ‘negative’ result mean?

Negative results (‘below the screen cut off’) are reassuring. These results indicate that the baby’s chance of having Down syndrome, Open Neural Tube Defects or Trisomy 18 is low. A negative result is correct 99.9% of the time, however, the chance that the baby is affected is not zero. In this situation, further diagnostic testing by amniocentesis would not be offered unless a woman is already eligible for amniocentesis based on age alone (age 40 or over). This is because the chance that the baby is affected is lower then the risk of pregnancy loss associated with the amniocentesis procedure itself.


What comes after a ‘positive’ result?

About 8-10% of all women who have MSS will have a ‘positive’ result, or, in other words, a result which is above the screen cut off. Even with a ‘positive’ screening result, most fetuses do not have a problem. It simply means that the chance for Down syndrome, neural tube defects, or Trisomy 18 is increased to a level which is sufficient to offer further testing (detailed ultrasound and/or amniocentesis). The vast majority of women who have a positive MSS result have healthy, unaffected babies.


How and when are results available?

Results are usually available 7-10 days after the second blood test (16-20w of pregnancy). All results above the screen cut off (positive) are telephoned to the midwife’s office for discussion. Accurate pregnancy dating is essential for this test, so a dating ultrasound is sometimes recommended before further follow-up. Options for follow up include genetic counselling to review the results and discuss further testing options and diagnostic testing (such as detailed ultrasound and/ or amniocentesis). Results below the screen cut off are sent by mail to the midwifery office and the result given to you as soon as possible.



Maternal Serum Screening (MSS) – Key points!

  1. The test is offered to all women
  2. The blood tests are performed at 10-14 and 15-21 weeks of pregnancy
  3. A Nuchal Translucency ultrasound is available at 10-14 weeks of pregnancy for women 35 and
  4. Maternal blood samples are used for the test
  5. If the screen result is ‘positive,’ follow up options include genetic counselling and further testing by detailed U/S and amniocentesis
  6. If dates are uncertain, a dating U/S performed early in the pregnancy can reduce false positives
  7. Women who will be 40 years of age at delivery can forego maternal serum screening as they can choose to go directly for amniocentesis if they wish


Advantages of MSS

  1. A negative result may offer some reassurance
  2. It may help in decision making. For example, if an Open Neural Tube Defect is detected before birth, heath care professionals can provide parents with information and support. They can plan for delivery in a specially equipped medical centre so that the baby can have any necessary surgery or treatment soon after


  1. MSS only screens for 3 things (Down syndrome, Trisomy 18, and neural tube defects only) and does not pick up every baby with those conditions
  2. Results take about 7-10 days to come back. This is an anxious time for many
  3. About 8-10% of all women get ‘positive’ results, however only 2-4% of all positives are true positives. Most women with a ‘screen positive’ result have normal
  4. A negative result does not guarantee that everything is all right with the
  5. Even if disability is confirmed by a diagnostic test (amniocentesis), it does not measure the degree to which the baby is
  6. Advanced maternal age also increases the risk for chromosomal abnormalities other than Down’s syndrome. There is no way of screening for all of these


Important questions to consider before choosing to have this screening test


(See Appendices 1 & 2)


  1. How do you feel about having a baby with a disability such as Down Syndrome, Spina Bifida or Trisomy 18?
  2. Would you want the type of information that this screening test can provide?
  3. If the result is ‘above the screen cut-off’ (otherwise ‘positive’), amniocentesis is an option. This test has a miscarriage risk of about 1 in 200 (0.5 %). Would this be an acceptable option for you?
  4. Consider whether knowing about a birth defect would change your medical, birthing or parenting plans. Would you consider termination if your baby had one of these problems?



What is Down Syndrome? (Trisomy 21)


Down syndrome is a condition caused by the presence of an extra chromosome. It is one of the most common genetic birth defects, affecting approximately 1 in 800 to 1000 babies. It can be hereditary or accidental. Down syndrome is a common cause of learning difficulty and is often associated characteristic facial features and certain medical problems. About 40-50% of affected individuals have congenital heart problems, and there is risk of ophthalmic (eye) and hearing impairment as well as thyroid and gastrointestinal problems. Life expectancy is sometimes reduced, however, many adults with this condition are now living into their 50’s and 60’s. The degree of learning difficulties is variable. There is no way to predict how serious any of the disabilities will be.


Children with Down syndrome usually can do most things that any young child can do, such as walking, talking, dressing and being toilet-trained. However, they generally start learning these things later than other children. The outlook for these children is far brighter than it once was. Today, an increasing number of adults with Down syndrome live semi-independently in community group homes where they take care of themselves, participate in household chores, develop friendships, partake in leisure activities and work in their communities.



Any woman at any age can have a baby with Down syndrome. However, the chance is higher the older the woman is. A woman who is 40 has a much higher chance of having a baby with Down syndrome than a woman who is 20. The father’s age may also affect the chance that the baby has Down’s syndrom, though research in this area is still ongoing. Because most women have their babies between 20 and 35, most babies with Down syndrome are born to younger women.


What is Trisomy 18? (Edward’s Syndrome)


This is a rare disorder caused by an extra chromosome at the 18th pair. Like trisomy 21 (Down syndrome), trisomy 18 affects all systems of the body and causes distinct facial features. It is estimated to occur in 1 in 6000 – 8000 live births. Most babies (95%) die before or within one hour of birth. Babies with this condition have severe mental disability and major physical problems and require skilled medical care. Infants have a 5% chance of surviving to age 1 year.


What is Spina Bifida?


This occurs when there is an opening in the spine which can cause nerve damage. Spina Bifida affects 1 in every 2000 live births each year in the US. It occurs more frequently among Hispanics and people of European descent and less commonly among Ashkenazi Jews, Asians and African-Americans.


Spina bifida varies in severity and in the level of disability. There is no way to predict exactly how serious these problems will be. This can range from individuals that lead full and active lives to individuals with physical disability which can include weakness or paralysis of the legs, incontinence, and hydrocephaly (fluid on the brain) which can cause mental developmental delays.


With treatment, children with spina bifida can usually become active individuals. At least 70% of children with spina bifida have normal intelligence, although some do have learning difficulties. A baby with the most severe form of spina bifida usually requires surgery within 24 to 48 hours after birth to tuck exposed nerves and spinal cord back inside the spinal canal and cover them with muscle and skin. Prompt surgery helps prevent additional nerve damage from infection or trauma.


There appears to be a hereditary factor and an increased risk for women who have had a previously affected pregnancy. However, 95% of babies born with spina bifida and other neural tube defects are born to parents with no family history of these disorders. There is also a possible increased risk for women who take anti-epileptic medications. The chance does not depend on the age of the mother. Ensuring adequate folic acid intake before and during early pregnancy is hugely protective.





Prenatal Diagnostic Tests


Diagnostic testing may be offered to you (all are optional) to see if your baby has a birth defect.


Who is offered diagnostic testing?


  • Women of “advanced maternal age.” This is considered to be pregnant women who will be 40 years or older at the time of delivery. However, in twin pregnancies, amniocentesis will be offered to women who are or will be 32 years or older at the time of
  • Couples who have received a positive maternal serum screening
  • Pregnancies initiated by intracytoplasmic sperm injection (ICSI).
  • Couples in which either person has had;
  • Another child or stillbirth with a chromosome abnormality
  • Another child with a neural tube defect such as spina bifida or anencephaly, or a close relative (brother, sister, niece or nephew) with a neural tube defect
  • Another child with a known or suspected genetic disorder, birth defect or developmental delay
  • Couples in which an ultrasound test has shown particular abnormalities in this
  • Couples in which either person is known to have a chromosome
  • Couples in which one or both partners have a known or suspected genetic disease or birth
  • Couples in which both partners are carriers or a genetic disorder, for example
  • Thalassaemia (more common in Mediterranean, Asian and East Indian populations)
  • Tay sachs (more common in the Ashkenazi jewish population)
  • Sickle cell anaemia (more common in the black population)
  • Cystic fibrosis (more common in the Caucasian population)
  • Women who have been exposed during pregnancy to certain drugs or other chemicals that may cause birth defects. This exposure could include women who have taken acutane (acne drug) or those who have used cocaine or alcohol heavily during
  • Couples with a family history of known or suspected genetic disorders, for example; Duchenne Muscular Dystrophy, Haemophilia, Myotonic Dystrophy or Fragile X


What tests are used?

  • Chorionic villus sampling (CVS) (not available in Victoria)
  • Amniocentesis
  • Detailed ultrasound


What is chorionic villus sampling? (not available in Victoria)


This is a newer alternative to amniocentesis for prenatal diagnosis. Chorionic villi form a tissue surrounding the amniotic sac and form the placenta.


CVS can be done as early as 10 weeks of pregnancy. The procedure involves inserting a narrow plastic tube through the vagina and cervix (done at 10 – 12 weeks) or inserting a slender needle through the abdominal wall (done at 10 weeks to term). As with amniocentesis, ultrasound is used to guide the catheter during the test. A small sample of placental tissue is then removed by gentle suction. The tissue is grown in the laboratory and examined under the microscope. Final results take approximately 2 –3 weeks.



  • CVS can detect chromosome
  • As with amniocentesis, if there is a family history of a known problem, other special tests may be done on the sample, however these have to be arranged in



  • CVS cannot detect neural tube defects. Further testing with detailed ultrasound and MSS are offered for this.
  • Mild problems including cramp and spotting happen occasionally. Vaginal spotting (bleeding) is more common after Trans-cervical CVS tests and is usually not
  • Approximately 1 in every 100 women who have CVS will have a miscarriage following the


  • There is a possible increased risk of limb abnormalities in the baby following CVS (an increase from 6 per 10,0000 births without CVS to a risk of 9 per 10,000 births after CVS).
  • CVS results are sometimes difficult to understand. In such cases, an amniocentesis test is usually offered to clarify the


What is Amniocentesis?


Amniocentesis is the most common test used for diagnosing a chromosome problem with the baby. It involves removing a small amount of the fluid which surrounds the baby in the amniotic sac. The test is relatively painless and is usually done after 15 weeks of pregnancy.


How is it done?

Amniocentesis is performed by an experienced obstetrician in a hospital on an outpatient basis. It involves inserting a needle through the mother’s abdomen (not through the navel) into the amniotic sac to take some of the fluid which surrounds the baby. Ultrasound is used to locate the baby and placenta. With the ultrasound picture on the screen, the specialist finds the safest and easiest place to insert the needle. The needle is then carefully guided to the selected spot and a small sample of fluid is slowly withdrawn through the needle. The fluid sample contains cells that the baby has shed from its skin and bladder. These cells are grown in the lab and then examined under a microscope. It takes 2 to 3 weeks before the results are available.



  • It is a diagnostic test (“yes or no” answer). It can detect Down Syndrome and other major chromosome abnormalities as well as Spina
  • If there is a family history of a known problem, other special tests may be done on the sample, however these have to be arranged in
  • It is considered a safe test for the



  • Although not usually serious, mild problems including cramping, bleeding and slight leakage of amniotic fluid happen occasionally in the
  • Although very rare, there is a small risk of injury to the
  • Approximately 1 woman in every 200 (0.5%) will have a miscarriage following the


What is ultrasound?


Ultrasound is helpful in giving important information about a pregnancy. It may be used early in a pregnancy (8-12 weeks) to find a normal heart beat, to identify twins or to predict the baby’s due date. It can be done at 10-14 weeks to provide a Nuchal Translucency measurement as part of a prenatal screen. A detailed ultrasound can be done later in the pregnancy (18 weeks) to look for structural problems in the baby and to see if the baby is growing normally. Ultrasound is also used during amniocentesis and CVS (see below) to locate the baby and placenta during the tests.


What are the risks?

Ultrasound is not an x-ray. Long term follow up has shown no differences in growth or development between those children whose mothers had a prenatal ultrasound and those who did not. Ultrasound safety has never been studied by randomised controlled trial, however, so it is recommended that pregnant women have only those ultrasounds that are medically necessary.