What is the OSCAR test?
What is OSCAR test?
- Fetal Medicine
- What is the OSCAR test?
Serum markers for early mothers (PAPP-A, free βhCG)
What are Maternal Serum Markers?
A maternal serum marker tests for chromosomal abnormalities such as trisomy 21 (Down’s syndrome) and trisomy 18 by measuring the components (PAPP-A, free βhCG) in the blood sample.
These chromosomal abnormalities are more likely to occur in older pregnant women, and it is recommended that the test be done between 15 and 17 weeks of pregnancy. Since this test is classified as a genetic screening test, the results are not 100% guaranteed. If you want a more accurate diagnosis, you need to take the CVS or Amniocentesis.
Why do we measure PAPP-A and free beta-hCG?
In the past, the differences between the various markers were presented at an international conference. The results showed that PAPP-A and free beta-hCG were the two most effective maternal serum markers for fetuses with Down syndrome. Later, several data showed that the combination of these two markers and accurately measured NT (swelling at the back of the neck) was the easiest and most accurate way to determine the probability. Currently, this combined test is used as an initial screening test all over the world. (Combinations of other markers are less accurate and less meaningful.
(Other combinations of markers are less accurate and less meaningful.) CRIFM started using this test internationally in 2000, and in Japan, CRIFM began to use it in 2009, and some facilities are currently using it in various regions. CRIFM presently performs the test in a domestic laboratory and provides results within a few hours after the blood is drawn, and those who test positive will be informed of the results the same day or the next day.
It will also be able to predict diseases other than trisomy (Preeclampsia).
A test combining maternal serum markers (PAPP-A, free beta-hCG) and NT (OSCAR test) is expected to detect trisomy and predict preeclampsia by adding a placental growth factor called PlGF. When preeclampsia occurs, there have been reports of fetus’s failure to thrive, intrauterine death, severe complications in pregnant women, and maternal death.
Currently, research on predicting preeclampsia by early serum markers is being conducted at facilities in Asia, including CRIFM. It is possible to combine testing for trisomy and preeclampsia with early maternal serum marker testing. Low-volume aspirin therapy is said to be effective for those who are at high risk for preeclampsia.
First trimester examinations at CRIFM
CRIFM can calculate the possibility of chromosomal abnormalities (21 trisomy, 18 trisomy, 13 trisomy) by combining “NT” and “maternal serum markers for early mothers (PAPP-A, free βhCG)” for those who have undergone Early fetal dock and wish to do so. The combination of these three tests is called the OSCAR test.
*If the blood test is done in the morning at the same time as the Early fetal dock, the test results will be available on the same day of the blood collection, or the next day if the blood is collected in the evening or later.
Maternal serum markers alone are not reliable
In fact, the blood test alone is not very meaningful.
This is because maternal serum markers (PAPP-A, free beta-hCG) alone can only detect chromosomal abnormalities about 65% of the time.
Therefore, CRIFM provides the option of serum marker testing only for pregnant women who undergo early fetal dock.
Many pregnant women in the early stages of pregnancy who have undergone early fetal dock and are found to have a low probability of chromosomal abnormalities request maternal serum markers.
However, if the result of early fetal dock is “high risk”, it is better to proceed to CVS for definitive testing without serum marker, because the fetal dock positive result rate is higher than that of serum marker combined test.
Measurement by a reliable instrument is important
The values of PAPP-A and free beta-hCG used in the initial combined test may vary slightly depending on the measurement device. CRIFM’s laboratories use internationally reliable instruments to measure PAPP-A and free beta-hCG.
In addition, only NT measured by qualified NT can be entered into the combined test, and the qualification number of the NT measurer (accredited by FMF in the UK) is required to perform the combined test. In Japan, there are only about 250 qualified NT, but CRIFM has 4 qualified NT, and multiple NT measurements are performed to increase the reliability.