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Large-for-Gestational-Age (LGA) Newborn

By Robert L. Stavis, PhD, MD, Clinical Director, Neonatal ICUs;Associate Professor, Department of Pediatrics, Main Line Health, Bryn Mawr, PA; Department of Pediatrics, Nemours/Alfred I. duPont Hospital for Children;Thomas Jefferson University Hospital

A newborn who weighs more than 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 or is obese.

  • Doctors take measurements of the mother's abdomen and use ultrasonography to take measurements of the fetus to help estimate the fetus's weight.

  • Large babies born to mothers with diabetes are more likely to be overweight as adults.

  • Cesarean delivery is sometimes necessary.

  • Complications are treated.

Gestational age refers to how far along the pregnancy is. The gestational age is the number of weeks that have passed since the first day of the mother's last menstrual period. This time frame is often adjusted according to other information doctors receive, including the results of early ultrasound scans, which give additional information regarding the gestational age. A baby is estimated to be due (the due date) at 40 weeks of gestation.

At a gestational age of 40 weeks, boys who weigh more than about 9 pounds 4 ounces (4.2 kilograms) are large for gestational age (LGA). Girls who weigh more than about 9 pounds 1 ounce (4.1 kilograms) are also LGA. Doctors use published growth charts to evaluate babies at other gestational ages.

Macrosomia (large body) is a related term used to describe infants who weigh more than 9 pounds 15 ounces (4.5 kilograms).

Causes

Large newborns may be normal babies who simply are large because the parents are large. However, certain problems in the mother sometimes cause babies to be large for gestational age.

The most common cause of large-for-gestational-age newborns is

Other risk factors for having large-for-gestational-age newborns include

  • Maternal obesity

  • Having had previous LGA babies

  • Genetic abnormalities or syndromes (for example, Beckwith-Wiedemann syndrome or Sotos syndrome)

  • Excessive weight gain during pregnancy (the fetus gets more calories as the mother gains more weight)

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

Symptoms

Symptoms of large-for-gestational-age newborns are mainly related to any complications that occur.

Complications

Common complications in large-for-gestational-age newborns include the following:

  • Birth injuries: Common injuries include stretching of the nerves in the shoulder (brachial plexus injuries) and fractures.

  • Difficult delivery: Vaginal delivery, especially if the fetus is in a breech presentation, may be difficult when the fetus’s head is large in comparison with the mother’s pelvis. Cesarean delivery (C-section) is commonly done for LGA infants.

  • Low Apgar score: The Apgar score is a rating of the baby's condition in the first minutes of life. LGA infants tend to have lower Apgar scores and are more likely to require assistance at birth.

  • Perinatal asphyxia: This complication is a decrease in blood flow to the baby before, during, or just after delivery. This complication may result from a problem with the placenta before or during delivery.

  • Meconium aspiration: LGA babies may pass meconium (dark green fecal material that is produced in the fetus's intestine before birth) in the amniotic fluid and take forceful gasps that cause the meconium-containing amniotic fluid to be breathed (aspirated) into the lungs.

  • Low blood sugar (glucose) levels (hypoglycemia): If the fetus has been exposed to high glucose levels because the mother's diabetes was poorly controlled during pregnancy, the fetus has a high level of insulin. At the time of delivery, the placental supply of glucose is abruptly stopped, and the high level of insulin can rapidly drop the baby's blood sugar level, resulting in hypoglycemia. Hypoglycemia may cause no symptoms, but some babies are lethargic and limp and some are jittery and hyperexcitable. Despite their large size, newborns of mothers with diabetes often do not feed well for the first few days.

  • Lung problems: Lung development may be delayed in newborns whose mothers have diabetes, and the babies are at increased risk of respiratory distress syndrome, even when they are not premature.

  • Birth defects: Infants of mothers with diabetes have an increased risk of birth defects, including ones that involve the brain, heart, kidneys, digestive tract, and lower part of the spine.

  • Excess red blood cells (polycythemia):LGA babies may have a higher blood count than usual. Too many red blood cells may cause the blood to become too thick, which may slow blood flow. Newborns with polycythemia have a reddish complexion and are sluggish. Polycythemia can contribute to hypoglycemia, respiratory distress, and hyperbilirubinemia.

Diagnosis

  • Before birth, measurement of the uterus and ultrasonography

  • After birth, assessment of gestational age and size and weight of the baby

During pregnancy, doctors measure the distance on the woman's stomach from the top of the pelvic bone to the top of the uterus (fundus). This measurement, called a fundal height measurement, corresponds roughly with the number of weeks of pregnancy. If the measurement is high for the number of weeks, the fetus may be larger than expected.

Ultrasonography can be used to assess the size of the fetus and estimate fetal weight to confirm the LGA diagnosis.

After birth, LGA is diagnosed by assessing the gestational age and the weight of the baby.

LGA newborns are assessed for any complications. Blood sugar is measured to detect hypoglycemia, and doctors do a thorough examination to look for birth injuries and structural or genetic abnormalities.

Prognosis

The most common problems of LGA infants (hypoglycemia, birth injuries, and lung problems) typically resolve over a few days with no long-term consequences.

As adults, LGA girls have an increased risk of having an LGA infant. All LGA infants are at risk of obesity and may have an increased risk of heart disease.

Treatment

  • Treatment of complications

There is no specific treatment for large-for-gestational-age newborns, but underlying conditions and complications are treated as needed.

Newborns with polycythemia are given intravenous (IV) fluids. If the polycythemia is severe, the physician may remove some blood and replace it with plasma (partial exchange transfusion), which dilutes the remaining red blood cells.

Newborns with hypoglycemia are treated with frequent feedings, or sometimes are given glucose by vein.

Respiratory distress and meconium aspiration are treated with supplemental oxygen or other supportive devices such as continuous positive airway pressure (CPAP—a technique allows newborns to breathe on their own while being given slightly pressurized oxygen) or a mechanical ventilator, depending on the severity of the problem.