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A newborn, whether delivered preterm, term, or postterm, whose weight is above that of 90% of newborns of the same gestational age at birth (above the 90th percentile) is considered large for gestational age.

• Newborns may be large because the parents are large or because the mother has diabetes.
• Large newborns born to mothers with diabetes are likely to be overweight as adults.
• Cesarean delivery is sometimes necessary.

Diabetes in mothers is the most common cause of large-for-gestational age newborns. Women who are obese or who have previously had a large infant are also at risk of having large-for-gestational age newborns. Some newborns are large for gestational age because of genetic factors, such as having rare syndromes (for example, Beckwith-Wiedemann syndrome or Sotos' syndrome).

The reason for excessive growth of the fetus varies but primarily results from an abundance of nutrients. In pregnant women with diabetes, a large amount of sugar (glucose) crosses the placenta (the organ that connects the fetus to the uterus and provides nourishment to the fetus) and results in high levels of glucose in the fetus's blood. The high levels of glucose trigger the release of increased amounts of insulin from the fetus's pancreas, resulting in accelerated growth of the fetus, including almost all organs except the brain, which grows normally.

Symptoms and Complications

Symptoms depend on which complications occur. Common complications include the following:

• Excess amount of red blood cells (polycythemia): Large-for-gestational-age newborns may have a ruddy complexion because too many red blood cells are produced. As the excess red blood cells are broken down, bilirubin is formed, which, along with poor feeding, results in jaundice (see Problems in Newborns: Underdeveloped Digestive Tract and Liver).
• Low blood sugar levels (hypoglycemia): In newborns of mothers with diabetes, the oversupply of glucose from the placenta stops abruptly at delivery when the umbilical cord is cut and the continuing rapid production of insulin by the newborn's pancreas leads to low levels of sugar in the blood (hypoglycemia). Often hypoglycemia causes no symptoms. Sometimes, newborns are listless, limp, or jittery. Despite their large size, newborns of mothers with diabetes often do not feed well for the first few days.
• Lung problems: Lung development is delayed in newborns whose mothers have diabetes. When these newborns are delivered by cesarean, they are at risk of developing lung problems. Newborns born prematurely are more likely to have immature diabetes are more likely to have immature lungs and to develop respiratory distress syndrome (see Problems in Newborns: Respiratory Distress Syndrome), even when born only a few weeks before full term.
• Increased risk of birth injuries: Newborns who are large for gestational age are at increased risk of birth injuries such as stretching of the nerves in the shoulder (brachial plexus injuries) and collarbone (clavicle) fractures. Vaginal delivery, especially breech deliveries, may be difficult when the fetus's head is large in comparison with the mother's pelvic measurements, which increases the risk of birth injury. Therefore, such a fetus may have to be delivered by caesarean.

Infants whose mother has diabetes also have a higher rate of birth defects than other newborns. Large-for-gestational-age newborns born to mothers with diabetes are likely to be significantly overweight later in childhood and as adults, which, along with their genetic predisposition, puts them at risk of developing type 2 diabetes (see Diabetes Mellitus (DM): Type 2).

Treatment

To treat hypoglycemia in newborns, intravenous glucose or frequent feedings by mouth or by tube into the stomach are often needed. Treatment of respiratory distress syndrome may require supplemental oxygen through a tube placed in the nose or intense intervention, such as respiratory support with a ventilator (see Problems in Newborns: Respiratory Distress Syndrome). Other complications may also require treatment, such as phototherapy for jaundice.