Integrated Screening Test
The integrated screening test is used to determine the chance that your baby may have Down syndrome or open neural tube defects, such as spina bifida. While there are other tests for these conditions, the integrated screening test is the most specific, has the highest detection rate and a low false-positive rate. Down syndrome may affect any pregnancy but some women are at higher risk than others, including those who:
- are older
- have given birth to another baby with Down syndrome
- have abnormalities involving chromosome 21
How is it performed?
The integrated screening test is performed in two stages:
- In the first stage you undergo an ultrasound, which helps us determine the gestational age and measure the thickness of the nuchal translucency (NT), the fluid-filled space at the back of the baby’s neck. A nurse will also take a blood sample to measure the amount of pregnancy-associated plasma protein-A. We perform the first stage between 11 and 13 weeks of pregnancy.
- In the second stage, a nurse will take a second blood sample to measure the amount of four proteins in your blood: alpha-fetoprotein, human chorionic gonadotropin, unconjugated estriol, and inhibin A. We perform the second stage ideally at 15 weeks of pregnancy and up to 22 weeks.
What happens afterward?
We combine the results from the first and second stages into a single screening result. The NT measurement, the levels of the five substances in your blood and your age help us estimate your risk of having a baby with Down syndrome. We can also use the screening results to estimate the risk for other disorders including open neural tube defects (spina bifida) and Trisomy 18.
The integrated screening results are usually ready one week after the second stage. We send a copy of the results to your health care provider, as well as schedule any specialist appointments you need and set a time for you to meet with a genetic counselor to discuss your options.
What do my results mean?
Results are considered “screen positive”—meaning your baby has a higher risk for Down syndrome than other babies—if the risk is one in 110 or greater (for example, one in 90 or one in 80). We then recommend amniocentesis so that we can examine your baby’s chromosomes. It is important to note that five of out every 100 women “screen positive;” however most will not have a baby with Down syndrome.
Results are considered “screen negative” if the risk for Down syndrome is less than one in 110 (for example, one in 150 or one in 200). Keep in mind that screening tests cannot diagnose or rule out specific conditions, only measure the chances of one affecting your baby.