Key Points

Low birthweight is when a baby is born weighing less than 5 pounds, 8 ounces.

Some low-birthweight babies are healthy, but others have serious health problems that need treatment.

Premature birth (before 37 weeks of pregnancy) and fetal growth restriction are the most common causes of low birthweight.

Being a person of color is not a cause for having a low birthweight baby. However, communities of color are disproportionately affected by racism. This affects their health and well-being and increases the risk of pregnancy complications.

Go to all your prenatal care checkups during pregnancy. Your health care provider tracks your baby’s growth and development at each visit.

Talk with your provider about what you can do to help reduce your risk for having a baby with low birthweight.

What is low birthweight?

Low birthweight is when a baby is born weighing less than 5 pounds, 8 ounces. Some babies with low birthweight are healthy, even though they’re small. But having a low weight at birth can cause serious health problems for some babies. A baby who is very small at birth may have trouble eating, gaining weight and fighting off infections. Some may have long-term health problems, too. About 1 in 12 babies (about 8 percent) in the United States is born with low birthweight.

What causes a baby to have a low birthweight?

There are two main reasons:

  • Preterm birth. 
  • Fetal growth restriction (also called intrauterine growth restriction or small for gestational age). This means a baby doesn’t gain the weight they should before birth. Some babies may have low birthweight simply because their parents are small. Others may have low birthweight because something slowed or stopped their growth during pregnancy. Your health care provider measures your belly and uses ultrasound to help track your baby’s growth during pregnancy. Ultrasound uses sound waves and a computer screen to show a picture of your baby while you’re pregnant.

If your provider thinks your baby’s growth is being restricted, you may have ultrasounds more often (every 2 to 4 weeks) to track your baby’s growth. Your provider also may do other tests such as heart rate monitoring and tests to check for infections or birth defects.. Babies who have birth defects are more likely to be born too early.

Are you at risk of having a low-birthweight baby?

Some things may make you more likely than others to have a low-birthweight baby. These are called risk factors. Having a risk factor doesn’t mean you’ll definitely have a low-birthweight baby, but it may increase your chances. Talk with your health care provider about what you can do to reduce your risk.

Medical risk factors for having a low-birthweight baby

  • Preterm labor. This is labor that starts too soon, before 37 weeks of pregnancy.
  • Chronic health conditions. These are health conditions that last for a long time or that happen again and again over a long period of time. Chronic health conditions need to be treated by a health care provider. Chronic health conditions that may lead to having a baby with low birthweight include high blood pressurediabetes and heart, lung and kidney problems.
  • Taking certain medicines to treat health conditions, such as high blood pressure, epilepsy and blood clots. Tell your provider about any prescription medicine you take. You may need to stop taking a medicine or switch to one that’s safer during pregnancy.
  • Infections. Certain infections, especially infections of the internal reproductive organs during pregnancy, can slow a baby’s growth in the womb. These include cytomegalovirusrubellachickenpoxtoxoplasmosis and certain sexually transmitted infections.
  • Problems with the placentaThe placenta grows in the uterus and supplies the baby with food and oxygen through the umbilical cord. Some problems in the placenta can reduce the flow of oxygen and nutrients to the baby, which can limit the baby’s growth.
  • Not gaining enough weight during pregnancy. Pregnant people who don’t gain enough weight during pregnancy are more likely to have a low-birthweight baby than those who gain the right amount of weight. If you have an eating disorder or have been treated for an eating disorder, tell your provider. Your provider can check on you and your baby carefully throughout pregnancy to help prevent complications and make sure you’re both healthy.
  • Having a baby who was born too early or who had low birthweight in the past.
  • Being pregnant with multiples (twins, triplets or more). More than half of multiple birth babies have low birthweight.
  • Smokingdrinking alcohol, using street drugs and abusing prescription drugs. Pregnant people who smoke are more than 3 times as likely to have a baby who weighs too little at birth than people who don’t smoke. Smoking, drinking alcohol, using street drugs, and abusing prescription drugs during pregnancy can slow the baby’s growth in the womb and increase the risk for preterm birth and birth defects.
  • Exposure to air pollution or lead
  • Being a member of a group that experiences the effects of racism and health disparities.
  • Domestic violence. This is when your partner hurts or abuses you. It includes physical, sexual and emotional abuse.
  • Age. Being a teen (especially younger than 15) or being older than 35 makes you more likely than other parents to have a low-birthweight baby.

Rates of low birthweight in the United States

Black babies are more likely than others to weigh less than they should at birth. The rates of low birthweight among different ethnic groups are:

  • About 1 in 7 Black babies (about 13 percent)
  • About 1 in 12 Asian babies (about 8 percent)
  • About 1 in 13 Native American or Alaska Native babies (about 8 percent)
  • About 1 in 14 Latinx babies (about 7 percent)
  • About 1 in 14 White babies (about 7 percent)

March of Dimes recognizes that racism and its effects are factors in the health disparities in pregnancy outcomes and babies’ health. We must work together to bring fair, just and full access to health care for all moms and babies.

Does a low birth weight cause problems for the baby?

Yes. Babies who weigh less than they should at birth are more likely than babies whose weight is normal to have health problems. Some need special care in a hospital’s newborn intensive care unit (also called NICU) to treat medical problems. These include:

  • Breathing problems, such as respiratory distress syndrome (also called RDS). Babies with RDS don’t have a protein called surfactant that keeps small air sacs in a baby’s lungs from collapsing. Treatment with surfactant helps these babies breathe more easily. Babies who have RDS also may need oxygen and other breathing help to make their lungs work.  
  • Bleeding in the brain (also called intraventricular hemorrhage or IVH). Most brain bleeds are mild and go away on their own. More severe bleeds can cause pressure on the brain that can cause fluid to build up in the brain. This can cause brain damage. In some cases, a surgeon may insert a tube into the baby’s brain to drain the fluid.
  • Patent ductus arteriosus. Patent ductus arteriosus is when an opening between 2 major blood vessels leading from the heart does not close properly. This can cause extra blood to flow to the lungs. In many babies who have patent ductus arteriosus, the opening closes on its own within a few days after birth. Some babies need medicine or surgery to close the opening.
  • Necrotizing enterocolitis. This is a problem in a baby’s intestines. The intestines are long tubes that are part of the digestive system. The digestive system helps the body break down food. Necrotizing enterocolitis can be dangerous for a baby and can cause feeding problems, swelling in the belly, and other complications. Babies who have necrotizing enterocolitis are treated with antibiotics and fed through an intravenous, or IV, tube. Some babies need surgery to remove damaged parts of intestine.
  • Retinopathy of prematurityThis eye disease is what happens when a baby’s retinas don’t fully develop in the weeks after birth.
  • Jaundice. This is a condition that makes a baby’s eyes and skin look yellow. It’s caused when there’s too much of a substance called bilirubin in the blood.
  • Infections. The immune system protects the body from infection. In a baby who is born too early, the immune system may not be fully developed and may not be able to fight off infection.

Does a low weight at birth cause problems later in life?

Babies who are born weighing too little may be more likely than others to have certain health conditions later in life, including:

  • Diabetes
  • Heart disease
  • High blood pressure
  • Intellectual and developmental disabilities
  • Metabolic syndrome
  • Obesity

If you’ve had a baby who weighed less than they should have at birth, talk with their health care provider about what you can do to help your baby be healthy. As your child grows, make sure they eat healthy food, stay active and go to all their health care checkups. Regular checkups can help your baby’s provider spot health conditions that may cause problems as your baby grows older. These checkups also help make sure that your child gets all the vaccinations they need to stay protected from certain harmful diseases.

If my baby has developmental delays, do they need early intervention services?

Yes. If your baby has developmental delays, it’s important to get early intervention services as soon as possible. Developmental delays are when your child doesn’t reach developmental milestones when expected. Early intervention services can help improve your child’s development. They can help children from birth through 3 years old learn important skills. Services include therapy to help a child talk, walk, learn self-help skills and interact with others.

The CDC program Learn the signs. Act early offers tools and information for parents who think their child may have developmental delays. You can find your state’s contact information for early intervention services. You don’t need a doctor’s referral or a medical diagnosis to ask for a free screening.

Last reviewed: June, 2021