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Screening choices

If your first visit with your health care provider is before 14 weeks (3 1/2 months) of pregnancy:

  • You can have: First Trimester Screening OR Integrated Prenatal Screening OR Serum Integrated Prenatal Screening.
  • The steps involved in each of these tests and their accuracy are described in the table below.

Test/Procedure(*) First Trimester Screening (FTS)Integrated Prenatal Screening (IPS)Serum Integrated Prenatal Screening (SIPS)

1st blood sample

11-14 weeks

11-14 weeks

11-14 weeks

* Nuchal translucency ultrasound

11-14 weeks

11-14 weeks

NONE

2nd blood sample

NONE

15-20 weeks

15-20 weeks

Results available

12-15 weeks

16-21 weeks

16-21 weeks

Detection rate
(accuracy)

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

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

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

False positive rate

About 3 to 9 out of 100 pregnancies (3-9%)

About 2 to 4 out of 100 pregnancies (2-4%)

About 2 to 7 out of 100 pregnancies (2-7%)

Diagnostic test if prenatal screening test is positive

CVS 11-13 weeks

If CVS is not available, you could have amniocentesisdiagnostic testing as described in the next column ›
Amniocentesis
15-22 weeks
Amniocentesis
15-22 weeks

Diagnostic test results available at:

    13-15 weeks

    17-24 weeks

    17-24 weeks

Abortion – if you decide to have this – could be performed at:

13-23 weeks
Timing will depend on local availability
17-23 weeks
Timing will depend on local availability
17-23 weeks
Timing will depend on local availability

OR Continuation with pregnancy

BirthBirthBirth
(*) First trimester screening is not available in all areas of Ontario
* 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 14 weeks of pregnancy.  The chance of a condition, like Down syndrome, is higher when the NT measurement is larger than expected.
NT ultrasound is available in most mid-size or larger cities.  If you live in an area where this special ultrasound is not available, you can still have SIPS.

If your first visit with your health care provider is after 14 weeks (3 1/2 months) of pregnancy:

  • You can have quadruple prenatal screening.
  • The steps involved in this test and its accuracy is described in the table below.
TestQuadruple Screening

Blood sample15-20 weeks
Results available16-21 weeks
Detection rate (accuracy)Of every 100 pregnancies with Down syndrome, about 75 to 85 will be detected (75-85%)
False positive rateAbout 5 to 10 out of 100 pregnancies (5-10%)
Diagnostic test if prenatal screening test is positive
Amniocentesis
15-22 weeks
Diagnostic test results available17-24 weeks
Abortion – if you decide to have this – could be performed at
17-23 weeks
Abortion timing will depend on local availability
OR Continuation with pregnancyBirth

For women over 35 years* of age at their due date:

Women 35 years of age and over at their due date can decide not to have a prenatal screening test but go directly to diagnostic testing such as CVS and amniocentesis.

Remember that screening tests give a better estimate of risk than age alone, for those aged 35 to 39.

In particular, women 40 and over should consider counselling about the pros and cons of screening and diagnostic testing.

For more information about diagnostic testing, talk to your health care provider or visit the sections of the website about chorionic villus sampling or amniocentesis.

*In some areas, this has changed and applies to women 40 years of age and over at their due date.

How accurate are prenatal screening tests?

Down syndrome

The detection and false positive rates in the table only refer to Down syndrome. This is because trisomy 18 is rare and we do not have exact numbers for it.

Trisomy 18

Generally, for all of the tests listed, the detection rate or accuracy is less for trisomy 18 than what it is for Down syndrome. Said another way, these tests are not quite as good at measuring the chance of having a baby with trisomy 18 (detection rate) as measuring the chance of having a baby with Down syndrome.

Open neural tube defects

Screening for open neural tube defects consists of a blood test done between 15-20 weeks. This is done as part of IPS, SIPS, Quad or as an additional blood test if a woman is having FTS. The ultrasound done at about 18 weeks of pregnancy also gives information about open neural tube defects. Of every 100 pregnancies with an open neural tube defect, 80 (or 80%) will be detected with prenatal screening.

Remember that most babies are born healthy.