FIRST & SECOND TRIMESTER ANTENATAL RISK ASSESSMENT packages or OSCAR (One-stop Clinic For Assessment of Risk for Fetal Anomalies)
Most babies are normal but a few may be born with major physical or mental disability due to chromosome abnormalities. The most common of such abnormalities is Down Syndrome. Diagnostic tests such as amniocentesis or chorionic villus sampling are the only way to be certain of chromosome abnormalities. However, these tests are associated with a risk of miscarriage. Fortunately, screening tests are available to determine the chance of the baby having specific chromosomal abnormalities like Trisomy 21 (Down Syndrome), Trisomy 18 (Edward’s Syndrome) and Trisomy 13 (Patau Syndrome). They are designed to help couples decide whether they wish to proceed to invasive diagnostic tests.
First Trimester Screening (FTS)
FTS combines maternal blood testing with an ultrasound evaluation of the fetus. This is performed between 11-14 weeks of pregnancy and the detection rate for chromosomal abnormalities is 90%.
- The ultrasound scan measures nuchal translucency (NT) which is a collection of fluid under the skin behind the baby’s neck in the first trimester of pregnancy. Down Syndrome babies tend to have a thicker than average NT. Results from this scan, the blood test and the mother’s age will determine the chances of chromosome abnormality.
- In addition to this, ultrasound assessment of the nasal bone at 11-14 weeks improves the accuracy of screening for Down Syndrome. The absence of a fetal nasal bone, along with a thickened NT, is associated with a higher chance of having a Down Syndrome baby.
Second Trimester Screening
Maternal serum screening is a blood test conducted between 15 and 20 weeks of pregnancy to aid in the risk assessment of Down Syndrome. The blood test measures the amount of human chorionic gonadotrophin (hCG) and alpha-fetoprotein (AFP) which are produced by the fetus and the placenta. These results are combined with the mother’s age to calculate the chance of having a Down Syndrome baby.
NON-INVASIVE PRENATAL TESTING (NIPT)
NIPT is a new test to screen for genetic conditions such as Down syndrome and certain other genetic disorders. There is no risk to the mother and fetus as it involves analyzing a sample of the mother’s blood for cell-free fetal DNA.