Whatever decision you making about testing in your pregnancy, it is a very personal decision and one that should be fully informed. There is no right or wrong choice. All testing in pregnancy is optional.
It is important to know that prenatal screening does not screen for all possible congenital anomalies and that all pregnancies have some risk for birth defects.
After considering “Is Prenatal Screening Right For Me?”, you have decided:
A. I do not want to have prenatal screening, now what?
Your health care provider will follow you as in any other pregnancy and make sure that both you and your baby are in the best possible health. Where available, you may be offered an ultrasound in the late first trimester (around 11-14 weeks gestation) for more accurate dating of your pregnancy, determination of twins, and early detection of major congenital anomalies. You may be offered an ultrasound in the second trimester at around 18-20 weeks gestation to look at the baby’s growth and anatomy.
B. I do not want to have prenatal screening but rather diagnostic testing, now what?
Your access to diagnostic testing will vary depending on where you live. If you, or in the case of a donor, the egg, will be 40 years or older at the time of delivery, you will likely have the option to choose diagnostic testing without prenatal screening. Talk to your health care provider about next steps.
C. I do want to have prenatal screening, now what?
Once you have decided to proceed with prenatal screening, the next step is for you and your health care provider to choose which testing option is right for you. Some factors that you need to consider when deciding which prenatal screening tests are available to you are:
1. Where you live
- Screening choices vary according to where you live. Your health care provider will discuss what is available.
2. How far along you are in the pregnancy
- Accurate dating of your pregnancy, determined by a first trimester ultrasound, is important for accurate screening results. Dating based on last menstrual period (LMP) is not ideal, but if a first trimester ultrasound is not available, this dating can be used.
- If the first prenatal visit with your health care provider is before 14 weeks (3 1/2 months) of pregnancy, options that may be presented to you include:
- Enhanced First Trimester Screening (eFTS)
- Serum only screening (options will vary according to where you live)
- Non-Invasive Prenatal Testing (NIPT)
- If the first prenatal visit with your health care provider is after 14 weeks (3-1/2 months) and before 21 weeks (~5 months) of pregnancy, options that may be presented to you include:
- Maternal Serum Quadruple Screening (MSS-Quad)
- Non-Invasive Prenatal Testing (NIPT)
3. The age of the pregnant person (or the egg in the case of a donated egg) when the baby is born
- If the pregnant person/egg donor will be 40 years of age or older at the time of birth, prenatal testing options include all screening tests above, in addition to the option of diagnostic testing
- If the pregnant person/egg donor will be 39 years of age or younger at the time of birth, prenatal options include all of the screening tests above, however NIPT would have to be paid for out of pocket and is not covered by Ontario Health Insurance Plan (OHIP). Diagnostic testing may not be offered at this time. (click here for the criteria for OHIP-covered NIPT)
Table 1 has an overview of the prenatal screening tests available in Ontario and how they compare to each other. Not all test options are available in all areas.
What is the NT measurement?
In addition to blood work, many screening tests also include an ultrasound measurement called the nuchal translucency (NT).
- The nuchal translucency (NT) is a fluid filled space at the back of every baby’s neck
- A larger NT measurement is associated with an increased chance for chromosome disorders like Down syndrome and some other genetic and non-genetic issues like congenital heart defect
- An ultrasound to measure NT is performed between 11 and 14 weeks of pregnancy and should be done at a certified ultrasound site. Your health care provider will tell you where an NT ultrasound can be obtained.
- An NT measurement of 3.5 mm or bigger is considered significant and would be a screen positive. A referral for genetic counselling will likely be offered.
When access to a certified ultrasound site to measure the nuchal translucency is not possible, serum-only prenatal screening (screening that only uses blood work) may be offered. The type and timing of serum-only screening is dependent on where you live.
Table 1. Available prenatal screening tests and how they compare.
Updated November 2018
Important Points to Consider:
Because prenatal screening is moving toward results available earlier in pregnancy, allowing expectant couples more time for decision making and access to additional services, integrated prenatal screening (IPS) is no longer available in Ontario. Most centres are now offering enhanced FTS (eFTS). This improved test performs better than traditional FTS with a higher detection rate and lower false positive rate. eFTS is expected to be just as good as IPS, but with results available earlier in pregnancy.
An ultrasound is recommended for all pregnant persons at about 18-20 weeks of pregnancy to look at the baby’s growth and anatomy, regardless of prenatal screening results. This ultrasound will act as the screening test for the detection of structural abnormalities in the baby, including open neural tube defects (oNTDs) such as open spina bifida, an opening in the baby’s spine. Screening for oNTDs using second trimester bloodwork is no longer available unless access to a good quality ultrasound examination is not possible.
While most babies are born healthy, 1 in 25 babies in Canada will be born with a difference that may require medical intervention.
It is important to remember that no test can detect every type of congenital anomaly.
I am expecting twins, are my testing options different?
If you are expecting twins, prenatal screening is available but in general is not as good as for pregnancies with one baby. Also, not all screening options will be available for a twin pregnancy. Talk to your health care provider for more about screening in a twin pregnancy.