Down’s syndrome screening is primarily done to screen for the chance that a fetus may have Down’s syndrome. The smaller the ratio of the Down’s screening value, the lower the chance of developing the condition and the better. The normal reference value for Down’s syndrome is usually around 1:270.
The normal range for the Down’s screening value, or risk value, is less than a 1:270 ratio. A value less than this means that there is a smaller chance of developing Down syndrome. If the Down screening value is higher than 1:270, it represents a high risk, with 1:270 to 1:1000 being the critical risk.
Due to the different reference standards set by each testing organization, Down’s syndrome screening values are not usually expressed as exact numbers, but are often just a ratio, and do not mean that the percentage is accurate.
The significance of the Down’s syndrome screening value is only a prediction of incidence and cannot accurately determine whether there is a developmental abnormality. If the Down’s syndrome screening value is high, further tests such as non-invasive DNA testing and amniocentesis should be performed.