SGA is a term used to describe a baby who is smaller than the usual amount for the number of weeks of pregnancy. SGA babies usually have birthweights below the 10^th percentile for babies of the same gestational age.

Some babies are small due to genetics (their parents are small); however, most SGA babies are small because of fetal growth problems that occur during pregnancy.

Many babies with SGA have a condition called intrauterine growth restriction (IUGR). IUGR occurs when the fetus does not receive the necessary nutrients and oxygen needed for proper growth and development of organs and tissues. IUGR can begin at any time in pregnancy.

SGA babies may appear physically and neurologically mature while being proportionately small (equally small all over) or normal length and size but have lower weight and body mass. SGA babies may be premature (born before 37 weeks of pregnancy), full term (37 to 41 weeks), or post term (after 42 weeks of pregnancy).

SGA is often identified before birth. During pregnancy, a baby's size can be estimated in different ways. If the baby measures to be smaller than expected they may be SGA.

Although many SGA babies have low birthweight, they are not all premature and may not experience the problems of premature babies.

Other diagnostic procedures include ultrasound, doppler flow, mother’s weight gain, and gestational assessment.