What is a small-for-gestational-age (SGA) baby?
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.
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Some babies are SGA just because it runs in their family
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Other babies are SGA because some problem kept them from growing as much as they should've in the womb (growth restriction)
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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
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Most SGA babies look like other babies born at the same gestational age, just smaller
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Most SGA babies catch up on their growth by age 1 year and reach the adult height they normally would
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Babies whose growth was restricted in the womb because of a serious problem are more likely to have problems later on
What causes a baby to be small for gestational age?
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:
Mother:
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Being very young (teenage) or very old
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Health problems, such as high blood pressure High Blood Pressure Each heart beat pushes blood through your arteries. Arteries are the blood vessels that carry blood from your heart to your body. Blood pressure is the pressure of blood in your arteries. Without... read more , diabetes Diabetes Diabetes is a disease in which your blood sugar (glucose) levels are too high. You get diabetes if your body's normal way of controlling blood sugar isn't working right. There are 2 types of... read more , kidney disease, or sickle cell disease Sickle Cell Disease Sickle cell disease is an inherited genetic abnormality of hemoglobin (the oxygen-carrying protein found in red blood cells) characterized by sickle (crescent)-shaped red blood cells and chronic... read more
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Using cigarettes, alcohol, or certain drugs during pregnancy
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Severe malnutrition
Pregnancy:
Fetus:
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Infections before birth, such as with cytomegalovirus Cytomegalovirus (CMV) Infection in Newborns Cytomegalovirus is a common virus that usually causes few or no problems but can cause serious illness in infants who are infected before birth or around the time of birth. Cytomegalovirus infection... read more , rubella Rubella Rubella is a contagious viral infection that typically causes mild symptoms, such as joint pain and a rash, but can cause severe birth defects if the mother becomes infected with rubella during... read more
, toxoplasmosis Toxoplasmosis in Newborns Toxoplasmosis is infection with the parasite Toxoplasma gondii. It usually does not cause problems in healthy adults, but it can cause serious illness in newborns and in people with a weakened... read more , or Zika virus Zika Virus Infection Zika virus infection almost never makes children or adults very sick. But Zika virus is very dangerous to an unborn baby (fetus). Zika can be spread by mosquitoes, sex, or blood transfusion... read more 
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Certain birth defects or genetic problems
What are the symptoms of a baby being small for gestational age?
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:
