"Microsomia" is defined as:
Birth weight below 90th percentile
Birth weight below 10th percentile
Birth weight below 20th percentile
Birth weight below 5th percentile
b. Birth weight below 10th percentile(Ref: Nelson's 20/e p 789-791, Ghai 8/e p 124-125)Microsomia is another name for a small for date (SFD) or small for gestational age (SGA) baby.SFD baby is a baby whose birth weight is less than 10th centile of expected according to the gestational age.
Newborn Infant - Physical Examination