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.
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.
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.
Advertisement
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy
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.
There are two main causes of low birth weight: premature birth and fetal growth restriction.
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, 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.
Factors that may increase your risk of having a baby with a low birth weight include:
Advertisement
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:
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.
Advertisement
Your baby’s healthcare provider will determine the necessary treatment for low birth weight. They’ll base treatment on your baby’s:
Treatment for low birth weight typically includes:
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.
You may be able to prevent your baby from being born with a low birth weight. During your pregnancy, make sure to:
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.
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.
Questions you can ask your healthcare provider include:
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.
Last reviewed on 05/12/2023.
Learn more about the Health Library and our editorial process.
Advertisement
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy