The screening results report will show the calculated risk values for trisomy 18, trisomy 21 and open neural tube defects, usually expressed as a ratio. Depending on the test method, hospitals use different scales for determining “high risk” and “low risk”. A high risk screening result means that the fetus has a higher chance of developing the disease, but it does not necessarily mean that the fetus is abnormal and further testing is needed to determine this. Similarly, a low risk indicates that the fetus has a low chance of developing the disease and that interventional prenatal diagnosis is not necessary. However, it is possible for a pregnant woman with a low risk screening to have a child with Down’s syndrome.