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 obesity.
Doctors take measurements of the mother's abdomen and use ultrasonography to take measurements of the fetus to help estimate the fetus's weight.
Cesarean delivery is sometimes necessary.
Complications are treated.
Large babies born to mothers with diabetes are more likely to be overweight as adults.
(See also Overview of General Problems in Newborns.)
Gestational age refers to the number of weeks of pregnancy. The gestational age is determined by counting the number of weeks between the first day of the mother's last menstrual period and the day of delivery. 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 LGA. Doctors use published growth charts or computer apps 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 of LGA Newborns
Large newborns may be healthy babies who simply are large because their parents are large. However, certain problems in the mother sometimes cause babies to be large for gestational age.
The most common cause of LGA newborns is
Other risk factors for having LGA 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 people who have poorly controlled 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 of LGA Newborns
Symptoms of large-for-gestational-age (LGA) newborns are mainly related to any complications that occur.
Complications
Common complications in LGA newborns include the following:
Birth injuries: Common injuries include stretching of the nerves in the shoulder (brachial plexus injuries) and fractures.
Low Apgar score: The Apgar score is a rating of the newborn's condition in the first minutes of life. LGA newborns tend to have lower Apgar scores and are more likely to require assistance at birth.
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.
Birth 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 or from difficulty delivering an LGA baby for reasons noted above.
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 newborns are lethargic and limp and some are jittery and very excitable. 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 newborns are at increased risk of respiratory distress syndrome or transient tachypnea of the newborn, even when they are not preterm.
Birth defects: Infants of mothers with poorly controlled 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 newborns 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 of LGA Newborns
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 a woman's abdomen from the top of the pubic 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 large-for-gestational-age (LGA) diagnosis.
After birth, LGA is diagnosed by assessing the gestational age and the weight of the newborn.
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.
Treatment of LGA Newborns
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 may be given intravenous fluids. If the polycythemia is severe, the doctor may remove some blood and replace it with saline (partial exchange transfusion), which dilutes the remaining red blood cells.
Newborns with hypoglycemia are treated with early (within 1 hour after birth) and frequent feedings, or sometimes are given glucose with fluids 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.
Prognosis for LGA Newborns
The most common problems of LGA infants (hypoglycemia, birth injuries, and lung problems) typically resolve over a few days with no long-term consequences.
LGA infants are at increased risk of obesity and may have an increased risk of heart disease.
As adults, women who were LGA at birth have an increased risk of having an LGA infant if they become pregnant.
