1. What is OSCAR?
- OSCAR is a mnemonic and stands for One Stop Clinic for Assessment of Risk for Downs syndrome. In many countries, it is named ‘first trimester combined nuchal translucency (NT) and biochemical screening’;
- It is a screening test performed at 11-13 6/7 weeks of gestation, mainly for Downs syndrome. It can also screen for Edwards and Patau syndrome
- The following parameters are obtained to calculate the risks of having a baby affected by Downs, Edwards or Patau syndrome for each individual woman:
- (i) The woman’s age;
- (ii) Her serum level of pregnancy-associated plasma protein-A (PAPP-A);
- (iii) Her serum level of free beta human chorionic gonadotrophin (free-beta hCG);
- (iv) Thickness of the baby’s neck-fold (nuchal translucency thickness)
2. How is OSCAR performed?
- Ultrasound for measuring the NT thickness of the fetus;
- Taking blood from the mother for the hormonal levels;
- All have to be performed at 11-13 6/7 weeks of gestation;
- A computer software will calculate the risks for Downs, Edwards and Patau syndromes based on the maternal age, NT and the levels of the hormones
3. How accurate is the test?
- The detection rates for Downs, Edwards and Patau syndromes are ~90%;
- There is a false positive rate of ~5%, meaning that 5% of all women with normal babies will have a positive result
4. What if the OSCAR results are abnormal?
- Not all women with abnormal results have abnormal babies. Approximately 5% of all women will have an abnormal result;
- The reasons leading to an increase in risk can be contributed by the woman’s age, the increase in NT, abnormal hormonal profile or a combination of any of the above. The implication can be different;
- It is important to discuss with a specialist in this field to determine the next appropriate option, whether it is NIPT, chorionic villus sampling or amniocentesis
5. What other abnormalities can OSCAR screen for?
- NT measurement is an essential part of the OSCAR test; there is a normal range of NT for different fetal size;
- Increase in NT is an important marker not just for fetal chromosomal abnormalities, but also for fetal structural defects, in particular congenital heart diseases. NT is also a good screening test for some genetic conditions
6. How is OSCAR compared with other antenatal screening tests for Downs syndrome?
Mid-trimester (16-20 weeks)
False positive rate