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Large for Gestational Age (LGA)

What is LGA?

Large for gestational age is a term used to describe babies who are born weighing more than the usual amount for the number of weeks of pregnancy. LGA babies have birthweights greater than the 90th percentile for their gestational age, meaning that they weigh more than 90 percent of all babies of the same gestational age.

The average baby weighs about 7 pounds at birth. About 9 percent of all babies weigh more than 4,000 grams (8 pounds, 13 ounces). Rarely do babies weigh over 10 pounds.

Although most LGA babies are born at term (37 to 41 weeks of pregnancy), a few premature babies may be LGA.

What causes LGA?

Some babies are large because their parents are large; genetics does play a part. Birthweight may also be related to the amount of weight a mother gains during pregnancy. Excessive weight gain can translate to increased fetal weight.

By far, maternal diabetes is the most common cause of LGA babies. Diabetes during pregnancy causes the mother's increased blood glucose (sugar) to circulate to the baby. In response, the baby's body makes insulin. All the extra sugar and the extra insulin production can lead to excessive growth and deposits of fat, thus, a larger baby.

Why is LGA a concern?

Because LGA babies are so large, delivery can be difficult. Delivery problems may include the following:

  • Prolonged vaginal delivery time

  • Difficult birth

  • Birth injury

  • Increased risk of cesarean delivery

Because many large babies are born to diabetic mothers, many problems of LGA babies are related to problems with glucose regulation. These may include the following:

  • Hypoglycemia (low blood sugar) of baby after delivery

  • Increased incidence of birth defects

  • Respiratory distress (difficulty breathing)

Many babies with LGA also have hyperbilirubinemia (jaundice or yellowing of the skin, eyes, and mucous membranes).

How is LGA diagnosed?

During pregnancy, a baby's birthweight can be estimated in different ways. The height of the fundus (the top of a mother's uterus) can be measured from the pubic bone. This measurement, in centimeters, usually corresponds with the number of weeks of pregnancy. If the measurement is high for the number of weeks, the baby may be larger than expected. Other diagnostic procedures may include the following:

  • Ultrasound (a test using sound waves to create a picture of internal structures) is a more accurate method of estimating fetal size. Measurements can be taken of the fetus' head, abdomen, and femur to estimate fetal weight.

  • A mother's weight gain can also influence a baby's size. Excessive maternal weight gain in pregnancy may correspond with a big baby.

Babies are weighed within the first few hours after birth. The weight is compared with the baby's gestational age and recorded in the medical record.

Treatment for LGA

Specific treatment for large for gestational age will be determined by your baby's doctor based on:

  • Your baby's gestational age, overall health, and medical history

  • Extent of the condition

  • Your baby's tolerance for specific medications, procedures, or therapies

  • Expectations for the course of the condition

  • Your opinion or preference

If ultrasound examinations during pregnancy show a fetus is quite large, some doctors may recommend early delivery. A planned cesarean delivery may also be recommended depending on the ultrasound estimate of the baby's weight.

After delivery, a LGA baby will be carefully examined for any birth injuries. Blood glucose testing is also performed to check for hypoglycemia. 

Prevention of LGA

Prenatal care is important in all pregnancies, especially to monitor fetal growth when a baby seems to be too small or too large. Examinations during pregnancy that show a large baby can help identify a mother who may have undetected diabetes, or other problems. Careful management of diabetes and proper weight gain, according to your doctor's recommendations, can help lower some of the risks to the baby.