Small for gestational age is used to refer to a baby who is smaller than the usual size for the number of weeks of pregnancy. These babies usually have the birth weights below the 10th percentile for babies of the same gestational age. They may appear physically and neurologically mature but are smaller than other babies of the same gestational age. SGA babies may be proportionately small (equally small all over) or they may be of normal length and size but have lower weight and body mass. This condition can occur in babies who are premature, full term or post term.