Diseases & Conditions


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Small for Gestational Age (SGA)


A newborn, whether delivered preterm, term, or postterm, whose weight is less than that of 90% of babies of the same gestational age at birth (below the 10th percentile) is considered small for gestational age.

There are several causes for this condition. In many cases, the newborn may be small simply because of genetic factors, such as having small parents (less commonly, a specific genetic syndrome associated with small stature may be involved). In other cases, the placenta may have functioned poorly, so that the fetus did not receive adequate nutrients and growth was impaired. This may happen if the mother has high blood pressure, preeclampsia, kidney disease, or long-standing diabetes. A viral infection, such as cytomegalovirus acquired before birth, may be responsible. Fetal growth may also have been impaired if the mother smoked or used alcohol or illicit drugs during the pregnancy (see Drug Use During Pregnancy ). Unless they have a genetic syndrome or viral infection, most small-for-gestational-age newborns have no symptoms. If the fetal growth was impaired because of poor placental function and inadequate nutrition, the newborn's growth may accelerate when provided with good nutrition after delivery. Some small-for-gestational-age newborns remain small as children and adults.

Last full review/revision February 2003

Source: The Merck Manual Home Edition