Early Prenatal Screening (first visit to health care provider is before 14 weeks of pregnancy)
If you have decided to have a prenatal screening test in the early stage of your pregnancy (before 14 weeks), you have the following options:
- You can have one of the new prenatal screening tests: First Trimester Screening, 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 at: |
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 amniocentesis diagnostic 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
Abortion timing will depend on local availability |
17 - 23 weeks Abortion timing will depend on local availability |
17 - 23 weeks Abortion timing will depend on local availability |
Or: Continuation with pregnancy |
Birth |
Birth |
Birth |
Note:
- FTS offers the earliest available results but requires a blood test for neural tube defects later in the pregnancy. FTS is not available in all communities. Please check with your health care provider.
- IPS and SIPS are a little more accurate than FTS and include screening for neural tube defects, but this is a 2-step process and results are available later in the pregnancy.
Nuchal Translucency (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.
*Nuchal Translucency 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.
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 Triple screening 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.
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