Low Birth Weight

Low birth weight means your baby was born weighing less than 5 pounds, 8 ounces (2,500 grams). It affects about 1 out of every 12 newborn babies. The main causes of low birth weight include being born premature and a condition called fetal growth restriction. Low birth weight can lead to a number of complications. If your baby is born with a low birth weight, they’ll likely need immediate treatment.

Overview

What is low birth weight?

If your newborn has a low birth weight, it means they were born weighing less than 5 pounds, 8 ounces (2,500 grams). Birth weight is your baby’s weight right after they’re born. Eighty out of every 100 babies born full term (37 to 41 weeks of pregnancy) weigh between 5 pounds, 11.5 ounces (2,600 grams) and 8 pounds, 5.75 ounces (3,800 grams).

Having a low birth weight doesn’t mean your child will be below average in weight when they grow up. In fact, some infants with a low birth weight are healthy even though they’re small.

But your baby’s birth weight can help their providers determine if they need extra attention immediately following birth. For some babies, having a low birth weight can cause serious health issues. If your baby is very small at birth, they may have issues eating, gaining weight and fighting off infections. Some babies may have long-term health problems, too.

How common is this condition?

In the United States, 311,932 babies were born with a low birth weight in 2021. That’s about 1 in every 12 babies, or 8.52% of all live births.

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Symptoms and Causes

What are the symptoms of low birth weight?

Infants born with a low birth weight look much smaller than babies born with a healthy, average birth weight. In addition, your baby’s head may look bigger than the rest of their body. They may also appear thin with little body fat.

What can cause low birth weight?

There are two main causes of low birth weight: premature birth and fetal growth restriction.

Premature birth

Premature birth, or preterm birth, means your baby was born before 37 weeks of pregnancy. If your baby was born early, it means they spent less time growing and gaining weight in your uterus. A fetus gains a lot of its weight during the last few weeks of pregnancy.

Fetal growth restriction

Fetal growth restriction, or intrauterine growth restriction (IUGR), means your baby didn’t grow and gain the weight they should have before birth. Some infants have low birth weight because their parents are small. But for others, IUGR can occur because something slowed down or stopped their growth during pregnancy. This can occur due to issues with the placenta, your health or your baby’s condition.

What are the risk factors for this condition?

Factors that may increase your risk of having a baby with a low birth weight include:

  • Chronic health issues during your pregnancy.
  • Having an infection during your pregnancy.
  • Taking certain medications during your pregnancy.
  • Using substances such as alcohol or tobacco during your pregnancy.
  • Not gaining or maintaining enough weight during your pregnancy.
  • Being pregnant with multiples.
  • Exposure to lead or air pollution.
  • Being Black or African American.
  • Being 17 or younger or 35 or older.
  • Preterm labor.
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What are the complications of this condition?

Newborns with low birth weight are at a higher risk of certain health issues. Their tiny bodies aren’t as strong as babies born of normal birth weight. They may have difficulty eating, gaining weight and fighting infection. In addition, babies with low birth weight frequently have trouble staying warm because they have so little body fat. The lower your baby’s birth weight, the higher their risk for complications. These may include immediate problems, including:

They also have a higher risk of developing long-term issues, such as:

  • Delayed motor and social development.
  • Learning differences.
  • Health conditions when they grow up, including high blood pressure, heart disease, obesity and diabetes.

Diagnosis and Tests

How is low birth weight diagnosed?

At your prenatal exams, your healthcare provider estimates the size of your baby in different ways. One way they keep track is by simply monitoring your weight gain. Another way they measure is by tracking fundal height. Fundal height is the distance from the top of your uterus to your pubic bone. Your provider may also use ultrasound to keep an eye on the fetus’s growth and development.

After birth, a healthcare provider will weigh your baby within the first few hours. They’ll compare your baby’s weight with their gestational age (how far along you were in pregnancy) and record it in their medical record. They’ll diagnose a baby weighing less than 5 pounds, 8 ounces (2,500 grams) as low birth weight. They’ll diagnose babies weighing less than 3 pounds, 5 ounces (1,500 grams) as very low birth weight.

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Management and Treatment

How is low birth weight treated?

Your baby’s healthcare provider will determine the necessary treatment for low birth weight. They’ll base treatment on your baby’s:

  • Gestational age.
  • Overall health.
  • Medical history.
  • Tolerance for medications, procedures or therapies.

Treatment for low birth weight typically includes:

  • Care in the hospital’s neonatal intensive care unit (NICU).
  • Use of a temperature-controlled bed.
  • Special feedings, sometimes through an intravenous (IV) line or with a tube into their stomach if your baby can’t suck.
  • Other treatments for complications.

Babies who are born with a low birth weight usually catch up in physical growth as long as there aren’t any other complications. Depending on your baby’s situation, their provider may refer them to a specialist for follow-up care.

Prevention

Can low birth weight be prevented?

You may be able to prevent your baby from being born with a low birth weight. During your pregnancy, make sure to:

  • Get regular checkups.
  • Get the correct amount of calories and nutrition.
  • Manage your blood sugar (if you have diabetes).
  • Avoid using substances such as alcohol and tobacco.

Outlook / Prognosis

What can I expect if my baby is born with a low birth weight?

If your baby is born with a low birth weight, they may need specialized care in the neonatal intensive care unit (NICU) of the hospital. They’ll stay in the NICU until they’ve gained enough weight and their providers think they’re well enough to go home.

Survival of newborns with low birth weight depends on how much your baby weighs at birth. Newborns weighing less than 1.1 pounds (500 grams) have the lowest survival rate.

Living With

How do I take care of my baby?

If your baby was born with a low birth weight, ask their healthcare provider what you should do to help them gain weight and be healthy. As your child gets older, make sure they’re eating healthy foods and staying active. It’s also important that they get to all of their well check-ups.

At routine well-check appointments, your baby’s provider can detect health conditions that may cause issues as they get older. Your child can also get all of their necessary vaccinations at their well check-ups. Vaccines can help them stay protected from certain harmful diseases.

What questions should I ask my healthcare provider?

Questions you can ask your healthcare provider include:

  • What can I do to reduce my risk of having a baby with a low birth weight?
  • If my baby was born with a low birth weight, what can I do to help them gain weight?
  • Will my child experience serious issues due to low birth weight?
  • Does my child need any tests or procedures?
  • What kinds of treatments do you recommend for my child?
  • Does my child need to take any medication?

A note from Cleveland Clinic

Some babies with a low birth weight are healthy even though they’re small. But your newborn’s birth weight can help their healthcare providers determine if they need any special attention immediately following birth. For some newborns, having a low birth weight can cause serious health issues. If your baby was born with a low birth weight, they may end up in the NICU. It can be difficult to see your tiny baby in the NICU. But place your trust in your baby’s healthcare providers. They’re doing everything they can to help your baby gain weight and get ready to leave the hospital.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 05/12/2023.

Learn more about our editorial process.

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