Gestation refers to pregnancy. Gestational age is how far along a mother is in her pregnancy. A full pregnancy lasts about 40 weeks (normal gestation). So a baby born 4 weeks early would have a gestational age of 36 weeks.
Small-for-gestational-age (SGA) refers to babies who weigh less than 9 out of 10 babies of the same sex at the same gestational age. It's important to compare weight by gestational age because the earlier a baby is born, the smaller it normally is. It's also important to compare babies of the same sex because girls tend to be a bit smaller than boys.
Some babies are SGA just because it runs in their family
Other babies are SGA because some problem kept them from growing as much as they should've in the womb (growth restriction)
Problems that can cause a baby to be SGA include placenta problems, using drugs during pregnancy, health problems in the mother or fetus, and lack of medical care during pregnancy
Most SGA babies look like other babies born at the same gestational age, just smaller
Most SGA babies catch up on their growth by age 1 year and reach the adult height they normally would
Babies whose growth was restricted in the womb because of a serious problem are more likely to have problems later on
Most SGA babies have no problems—they just happen to be small. Often lots of other people in their family are small too.
Many things raise the chances of having an SGA baby:
SGA babies weigh less than 90% of babies their same gestational age. At full term, SGA boys weigh less than about 6 pounds 9 ounces (3000 grams), and SGA girls weigh less than about 6 pounds 3 ounces (2800 grams).
Otherwise, SGA babies tend to look the same as other babies the same gestational age unless their growth was severely restricted. Then they may:
Small babies who are healthy do not need any treatment.
Doctors will treat any complications that develop. Your baby may need: