Integrated Prenatal Screening (IPS)
This screening test combines measurements from a nuchal translucency ultrasound and two blood tests to estimate the chances of a developing baby having Down syndrome.
The IPS takes into account the measurement of the ultrasound and the level of the proteins and other substances measured in the blood tests. It then adjusts for the woman’s age and gives a numerical estimate of the chance of Down syndrome, such as 1/2000 or 1/8.
In addition, unlike the first trimester screening assessment (FTS) which also screens for Down syndrome, the IPS will determine if there is an increased chance of spina bifida.
The ultrasound and first blood test are done at Mount Sinai between 11 weeks, 2 days and 13 weeks, 3 days of pregnancy. The second blood test is done between 15 – 18 weeks.
The results of the IPS are sent to your caregiver (obstetrician, family doctor or midwife) about 1 week after the second blood test.
Results are categorized as either screen positive or screen negative.
If the test indicates the chance for Down syndrome is greater than 1/200, the result is called screen positive. The test will also indicate a screen positive for Trisomy 18/13 if the chance of chromosome abnormalities Trisomy 18 and Trisomy 13 is greater than 1/100.
Approximately 2 - 3% of women taking this test will screen positive, but the majority of these women will NOT be carrying a pregnancy affected with Down syndrome (also known as a false positive result). Only a small proportion will be affected with Down syndrome (a true positive).
The chance a woman will screen positive also increases with her age, because the rate of Down syndrome pregnancies increases as a woman ages.
Close to 90 per cent of the pregnancies affected with Down syndrome will screen positive.
A less than 1/200 chance of Down syndrome is a screen negative result, and more than 99% of pregnancies WITHOUT Down syndrome will screen negative.
However, about 10% of pregnancies with Down syndrome will also screen negative (false negative), meaning results are not absolutely guaranteed.
Advantage of IPS
Results from an IPS offer a lower false positive rate than a first trimester screening assessment, meaning fewer women will be offered an unnecessary amniocentesis (carrying a 0.5-1% risk of miscarriage).
IPS also includes a screen for spina bifida as part of the second blood test.
Disadvantage of IPS
Screening results from an IPS are not available until the second trimester of pregnancy, which delays decision making about further testing (such as amniocentesis), and thus diagnosis.