Traditional screening for Down syndrome has been testing in either the first or second trimester. Combining tests from both trimesters, to perform integrated screening, provides a higher detection rate of abnormal pregnancies with fewer positive results (and fewer amniocenteses). Integrated screening is the newest advance in the field of prenatal screening.
Comprehensive Integrated Screening
Integrated screening estimates each woman's unique risk of fetal Down syndrome by combining both first and second trimester screening tests with maternal age. It involves two steps:
- Step One: The first trimester screening test — performed between 10 weeks 4 days and 13 weeks 6 days; Maternal blood test for Pregnancy-Associated Plasma Protein-A (PAPP-A) and ultrasound for fetal nuchal translucency.
- Step Two: The quad screen — ideally performed at 15-17 weeks (but possible up to 22 weeks).
After the second step is completed, the results of both tests are combined, and a single result is provided. Approximately 95% of women with a fetus with Down syndrome or Trisomy 18 will have a screen positive test result showing an increased risk.
Serum Integrated Screening
Although the highest detection rate is achieved by the comprehensive integrated screening test, serum integrated screening is an alternative. This approach uses only maternal blood tests (PAPPA in Step One; AFP, hCG, estriol, and inhibin in Step Two) to estimate the risk of Down syndrome and Trisomy 18. Approximately 85-87% of women with a fetus with Down syndrome and 90% with Trisomy 18 will be identified as at an increased risk. Because a specialized ultrasound exam is not necessary for serum integrated screening, a patient visit to UAB is not required. Samples can be sent to our lab from any physician's office. The first blood sample should be drawn at between 11 weeks 0 days gestation and 13 weeks 6 days, and the second sample at between 15 and 18 weeks gestation.
Do I have to wait until the second trimester test is complete before I receive any results?
The most accurate screening results are obtained when both first and second trimester screening tests are performed, and the final risk estimate is determined after the second trimester screening test is completed. There are fewer false positive test results when information from both the first and second trimester tests is used (compared to either the first or second trimester tests alone).
Fewer false positive results mean fewer amniocenteses and, therefore, less risk of pregnancy complications. However, some patients may have such a high risk of Down syndrome after the first step of testing that it is unlikely that the second step would change their ultimate risk estimate. In this case, results of the first step (the first trimester screening test) will be reported so that the women can have the option of undergoing a diagnostic test (CVS or amniocentesis) earlier.
What if I do not return for my second blood test?
If you do not return to have your second blood test performed, we cannot perform an integrated screening test. We will try to contact you and your doctor or clinic if we do not receive a sample by the recommended date, but if we do not receive the blood sample, a risk will be given based on the information from the first stage only.
Integrated screening offers patients the highest detection rate at the lowest false-positive rate of any screening test for fetal aneuploidy. UAB has established a clinic to make comprehensive integrated screening available to patients. Click here to learn more.