Current labels are incorrect:
"Small for gestational age (<-2SD)" (defn: Birth weight less than 10th percentile)
"Large for gestational age (>+2SD)" (defn: Birth weight > 90th percentile)
However, +/- 2SD is the threshold used for things that are in the most extreme 3% (e.g. 'Birth length less than 3rd percentile' is displayed as 'Small birth length (<-2SD)'), and conforms to a normal distribution. A more accurate threshold would be 1.3 SD, which is actually quite a large difference.