What is large for gestational age (LGA)?

Large for gestational age (LGA) is used to describe newborn babies who weigh more than usual for the number of weeks of pregnancy. Babies may be called large for gestational age if they weigh more than 9 in 10 babies (90th percentile) of the same gestational age. In the U.S., babies that weigh over 8 pounds, 13 ounces (4,000 g) are at the 90th percentile for weight when they are born at 40 weeks gestation.

Babies born earlier than 40 weeks are considered LGA at lighter weights. Babies born after 40 weeks are considered LGA at slightly higher weights. Overall, babies born in the U.S. in recent years weigh a little more than they used to. Normal ranges for birth weight may also be different, based on ethnic background.

What causes babies to be LGA?

Some babies are large because their parents are large. Parents may pass along this trait to their children. A high birth weight can also be related to the amount of weight a birth parent weighed before pregnancy or gains during pregnancy. Pregnant people who weigh more or gain a lot of weight during pregnancy often give birth to babies who are large for gestational age. Gene factors may also make a baby more likely to be LGA.

But diabetes in the pregnant person is the most common cause of babies who are large for gestational age. When a pregnant person has high blood sugar, they can pass that along to their baby. In response, the baby's body makes insulin. All the extra sugar and the extra insulin that is made can lead to fast growth and deposits of fat. This means a larger baby. It also means a risk for low blood sugar right after birth. At that point, the pregnant person's supply is no longer there, but the baby's insulin levels stay high.

What are the symptoms of LGA?

Babies may be called large for gestational age if they weigh more than 9 in 10 babies of the same gestational age.

How is LGA diagnosed?

Babies with this problem are often diagnosed before birth. During pregnancy, a baby’s size can be estimated in different ways. The height of the top of the pregnant person’s uterus can be measured from the pubic bone. This measurement in centimeters usually links with the number of weeks of pregnancy after the 20th week. If this measurement is high for the number of weeks, the baby may be larger than expected. Before the baby is born, healthcare providers use the term fetal macrosomia instead of LGA.

Other ways to check the baby’s growth before birth include:

• Ultrasound. This test uses sound waves to create a picture of your baby and the inside of your body. It is a more accurate method of estimating the size of your baby, but it's still not exact. Measurements can be taken of your baby’s head, belly (abdomen), and upper leg bone to see how fast they are growing.

• Weight gain during pregnancy. This can also affect your baby's size. Gaining a lot of weight during pregnancy may cause your baby to be bigger than normal.

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.

How is LGA treated?

Treatment will depend on your child’s symptoms, age, and general health.

If ultrasound exams during pregnancy show that your baby is very large, your healthcare provider may recommend early delivery. You may need a planned cesarean section.

After birth, a baby who is large for gestational age will be carefully checked for any injuries that happened during birth. Your baby may have blood glucose testing for at least the first 12 hours to check for low blood sugar.

What are possible complications of LGA?

If a baby is too large to fit through the birth canal easily, birth can be difficult. Problems at birth may include:

• Long time for delivery

• Difficult birth

• Injury to the baby, such as a broken collar bone or damaged nerves in the arm (brachial plexus)

• Increased need for a cesarean section delivery

Many large babies are born to pregnant people with diabetes. Poor control of blood sugar may cause problems, such as:

• Low blood sugar in the baby in the first several hours after birth

• A higher risk for birth defects

• Trouble breathing

Babies who are large for gestational age are at higher risk for a breathing problem called respiratory distress syndrome. They also may be at risk of breathing meconium into the lungs around the time of birth.

Birth injuries, such as a broken collar bone or damaged nerves in the arm (brachial plexus), are more common in babies who are very large for gestational age. These babies also may need to stay in neonatal intensive care because of breathing problems, low blood sugar (hypoglycemia), or both. The risk for problems increases as the birth weight increases. The risks are highest for babies who weigh more than 9 pounds, 11 ounces (4,400 g).

LGA babies are more likely to have an excessive amount of red blood cells (polycythemia). As these red blood cells break down, the liver may not be able to handle the increased amount of bilirubin needing to be conjugated. This may lead to high levels of bilirubin in the blood, resulting in jaundice.

How can LGA be prevented?

Regular prenatal care is important in all pregnancies. Regular checkups can help your healthcare provider find out how your baby is growing. If your baby seems large, it may be a sign that you have undetected diabetes or other problems. To lower some of the risks to your baby:

• Take care of your diabetes.

• Watch your weight.

• Follow your healthcare provider’s advice.

Key points about large for gestational age

• Babies are called large for gestational age if they weigh more than expected for their gestational age (weeks of pregnancy) at birth.

• Diabetes is the most common cause of babies who are large for gestational age.

• If a baby is too large to fit through the birth canal easily, delivery can be difficult.

• If ultrasound exams during pregnancy show a baby is very large, your healthcare provider may recommend early delivery.

• Regular prenatal checkups can help your healthcare provider find out if your baby is too large.

Next steps

Tips to help you get the most from a visit to your child’s healthcare provider:

• Know the reason for the visit and what you want to happen.

• Before your visit, write down questions you want answered.

• At the visit, write down the name of a new diagnosis and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you for your child.

• Know why a new medicine or treatment is prescribed and how it will help your child. Also know what the side effects are.

• Ask if your child’s condition can be treated in other ways.

• Know why a test or procedure is recommended and what the results could mean.

• Know what to expect if your child does not take the medicine or have the test or procedure.

• If your child has a follow-up appointment, write down the date, time, and purpose for that visit.

• Know how you can contact your child’s healthcare provider after office hours, and on weekends and holidays. This is important if your child becomes ill and you have questions or need advice.