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Prenatal Screening

What is prenatal screening?​ 

Prenatal screening is a way for you to determine if your baby is at increased risk for a chromosome difference such as trisomy 21 (Down syndrome) or trisomy 18. Trisomy 21 and 18 can affect anyone in any pregnancy regardless of their family history. The chance of them happening increases with age.​

Depending on the prenatal screening you choose, it can also tell you whether your baby is affected by other genetic conditions, such as trisomy 13, or sex chromosome differences. 

Chromosomes are made of DNA, and people with a chromosome difference may have an extra chromosome or may be missing chromosome material.​

Prenatal screening tells patients if there is a chance of these chromosome differences. It cannot tell definitively if there is a difference. ​

Diagnostic testing is required to definitively tell if there is a difference in the baby.


How is Prenatal Screening Completed?​

  • Prenatal screening is non-invasive, and can be completed by bloodwork. However, it is a screening test, and cannot provide diagnostic information.​

  • Prenatal screening is available to all Nova Scotians, and can be ordered through your health care provider.​

  • Prenatal screening can be completed as early as 10 weeks gestational age. The types of prenatal screening available depend on what gestational age you are in pregnancy, your age, when you first see your health care provider, and whether you have twins/multiples.​

  • If you are over the age of 35, you are eligible for an early ultrasound in the Fetal Assessment and Treatment Center at 11-14 weeks gestational age. This ultrasound would measure the nuchal translucency of the baby, which helps assess the risk for chromosome differences.


Types of Provincially Funded Prenatal Screening:​

  1. Maternal Serum Testing (MST) – This testing is funded by provincial health insurance (ex: MSI).  It consists of two blood tests.  The first is completed in the first trimester (9-13+6 weeks gestational age) and the second is completed in the second trimester (15-20+6 weeks gestational age).  The second trimester blood test needs to be completed in order to have a finalized report, which will provide a risk assessment for trisomy 21, trisomy 18, and spina bifida. ​

    • If the first trimester bloodwork is not done, the second trimester bloodwork can still be completed.​

    • If a patient qualifies for nuchal translucency measurement, which is completed at 11-14 weeks gestational age, the measurement is combined with the MST results to increase the accuracy of the screen.​

  2. Non-invasive Prenatal Screening (NIPS) – For some patients (ex: twins detected in the second trimester, previous pregnancy affected by certain chromosome differences, or high risk MST for trisomy 21), this testing is funded by provincial health insurance (ex: MSI). It detects fetal DNA in the maternal bloodstream, and is slightly more accurate than Maternal Serum Testing. It can be completed at any time in the pregnancy after 10 weeks gestational age. It only needs to be completed once.


Types of Privately Funded Prenatal Screening:

  1. Non-invasive Prenatal Screening (NIPS) – This test detects fetal DNA in the maternal bloodstream and is slightly more accurate than Maternal Serum Testing (MST). It can be completed at any time in the pregnancy after 10 weeks gestational age. It only needs to be completed once. Any pregnant individual can have this test completed for prenatal screening, and the results can be reported sooner than the MST. ​
    • To complete this testing, a dating ultrasound is preferred to confirm pregnancy dating and viability.​
    • A requisition is required from your health care provider. The requisition and bloodwork are sent to a company and the result is sent to your email.​
    • Standard NIPS screens for trisomy 21, trisomy 18, trisomy 13, and sex chromosome differences.  It will tell you the sex of your baby if that is something you would like to know.


How do I know if prenatal screening is right for me?​

All pregnant patients have the option to pursue prenatal screening. It is an individual choice. Some people would like to know if their baby is affected by a chromosomal difference early in pregnancy, while others may not want to have this information in pregnancy. ​

Some questions to ask yourself could be:​

  • Would you want to know this information to help you prepare for the pregnancy?​

  • If a result was positive, would you want to confirm it with a diagnostic test?​

  • If your baby was diagnosed with a chromosome difference, would you want to continue the pregnancy?​

  • It's your choice whether or not to have prenatal genetic screening. ​

The earlier you complete prenatal screening, the more options and time you have in your pregnancy to decide what to do with that information.


What do the results of the different types of prenatal screening mean?​

  • If Maternal Serum Testing was completed, the results are provided after the second trimester bloodwork is drawn. Risks are calculated for Trisomy 21, Trisomy 18, and open neural tube defects. ​

    • If the risks calculated are less than the “cut-off” risk, the screen will be reported as negative. ​

    • If the risks calculated are more than the “cut-off” risk, the screen wll be reported as positive.​

    • If the screen is positive, you may either be eligible for provincially funded NIPS, or an ultrasound in the Fetal Assessment Treatment Center (FATC).​

  • If the Non-invasive Prenatal Screening (NIPS) was completed, the results will be provided directly to you. The risks are calculated for trisomy 21, trisomy 18, and trisomy 13. ​

    • The result will either be labeled as “high-risk” or “low-risk” for trisomy 21, trisomy 13, or trisomy 18. ​

    • If the result is “high-risk”, the health care provider who ordered the test will contact you, and you may be eligible for an ultrasound in the FATC.


What do I do if the prenatal screening result is positive?​

This results does not mean your baby has trisomy 21, trisomy 18, trisomy 13 or an open neural tube defect. Most pregnant individuals with this result do not have a baby affected with one of these conditions. However, your risk of having a baby affected with one of these conditions is higher than the average person.​

Your health care provider will reach out to you. If you are close to 18-20 weeks gestation, you may have a detailed anatomical ultrasound arranged in FATC. A normal ultrasound can reduce your risk.​

If you had Maternal Serum Testing (MST) completed, and the risk for trisomy 21 is still positive after a normal ultrasound, you are eligible for funded Non-Invasive Prenatal Testing. Although this is also a screen, it is more accurate than MST.​

You may want to confirm the results of the prenatal screen with a diagnostic test.


What diagnostic tests are available?​

The diagnostic test available depends on your gestational age. They are considered invasive procedures and have an extremely small chance of pregnancy loss.​

  • Chorionic Villi Sampling (CVS): 

    • Chorionic villus sampling is an invasive test where a needle is either placed into the placenta through the abdomen or the vagina. The needle is used to collect a small piece of the placenta.  The procedure is guided by ultrasound.​

    • This test is completed at 11-14 weeks gestational age.​

    • The risk of miscarriage is 1%.​

  • Amniocentesis:​

    • Amniocentesis is an invasive test where a needle is placed through the abdomen to collect a small amount of amniotic fluid. ​

    • This test is completed after 15 weeks gestational age.​

    • The risk of miscarriage is 0.5%.

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