Low birthweight


  • 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.

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

  • Talk to 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 being low birthweight can cause serious health problems for some babies. A baby with low birthweight may have trouble eating, gaining weight and fighting off infections. Some low-birthweight babies 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 be born with low birthweight?

There are two main reasons why a baby may be born with low birthweight:

  1. Premature birth. This is birth that happens too soon, before 37 weeks of pregnancy. Being born too early means a baby has less time to grow and gain weight in the womb. The earlier a baby is born, the lower her birthweight may be. About 1 in 10 babies in this country is born prematurely each year. Talk to your health provider about things you can do to help reduce your risk of having a premature baby.
  2. Fetal growth restriction (also called FGR, growth-restricted, small for gestational age, SGA and small for date). This means a baby doesn’t gain the weight she should before birth. Some growth-restricted babies may have low birthweight simply because their parents are small. Others may have low birthweight because something slowed or stopped their growth in the womb. 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 inside the womb. If your provider thinks your baby is growth-restricted, you may get ultrasounds more often (every 2 to 4 weeks) to track your baby’s growth. Your provider also may do other tests like heart rate monitoring and tests to check for infections. In some cases, treating health conditions in the mom during pregnancy can help improve a baby’s growth.

Premature birth and fetal growth restriction may be caused by conditions that affect your baby in the womb, like infections and birth defects. Birth defects are health conditions that are present at birth. Birth defects change the shape or function of one or more parts of the body. They can cause problems in overall health, how the body develops, or how the body works. They may limit a baby’s development in the womb, which may lead to low birthweight. Babies with birth defects are more likely than babies without birth defects to be born prematurely.

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

We know 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 for sure that you’ll have a low-birthweight baby. But it may increase your chances. Because many premature babies are born with low birthweight, many risk factors for preterm labor and premature birth are the same as for having a low-birthweight baby. Talk to your health care provider about what you can do to help 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 treatment from a health care provider. Chronic health conditions that may lead to having a baby with low birthweight include high blood pressure, diabetes and heart, lung and kidney problems.
  • Taking certain medicines to treat health conditions, like 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 in the uterus (womb) during pregnancy can slow a baby’s growth in the womb. These include cytomegalovirus, rubella, chickenpox, toxoplasmosis and certain sexually transmitted infections (also called STIs, sexually transmitted diseases or STDs).
  • Problems with the placenta. The placenta grows in your uterus and supplies your baby with food and oxygen through the umbilical cord. Some problems in the placenta can reduce the flow of oxygen and nutrients to your baby, which can limit your baby’s growth.
  • Not gaining enough weight during pregnancy. Women who don’t gain enough weight during pregnancy are more likely to have a low-birthweight baby than women 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 premature baby or a growth-restricted baby in the past
  • Being pregnant with multiples (twins, triplets or more). More than half of multiple birth babies have low birthweight.

Risk factors in your everyday life for having a low-birthweight baby

  • Smoking, drinking alcohol, using street drugs and abusing prescription drugs. Pregnant women who smoke are three and a half times more likely to have an SGA baby than women who don’t smoke. Smoking, drinking alcohol, using street drugs and abusing prescription drugs during pregnancy can slow your baby’s growth in the womb and increase the risk for premature birth and birth defects.
  • Exposure to air pollution or lead
  • Low socioeconomic status (also called SES). SES is a combination of things like your education, your job and your income (how much money you make).
  • Domestic violence. This is when your partner hurts or abuses you. It includes physical, sexual and emotional abuse.

Age and race as risk factors for having a low-birthweight baby

Being a teen mother (especially younger than 15) or being older than 35 makes you more likely than other women to have a low-birthweight baby. In the United States, black women are more likely than others to have a low-birthweight baby. The rates of babies born with low birthweight each year 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 American Indian/Alaska Native babies (about 7 percent)
  • About 1 in 14 Hispanic babies (about 7 percent)
  • About 1 in 14 white babies (about 7 percent)

We don’t know exactly why race plays a role in having a low-birthweight baby; researchers are working to learn more about it.

What health problems are common in low-birthweight babies?

Low-birthweight babies are more likely than babies with normal weight to have health problems as a newborn. Some need special care in a hospital’s newborn intensive care unit (also called NICU) to treat medical problems. These include:

  • Breathing problems, like 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 with 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 fix themselves with no or few lasting problems. 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 (also called PDA). PDA is when an opening between two major blood vessels leading from the heart does not close properly. This can cause extra blood to flow to the lungs. In many babies with PDA, the opening closes on its own within a few days after birth. Some babies with PDA need medicine or surgery to close the opening.
  • Necrotizing enterocolitis (also called NEC). 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. NEC can be dangerous for a baby leading to feeding problems, swelling in the belly and other complications. Babies with NEC are treated with antibiotics (medicines that kill infections) and fed intravenously (through a vein) instead of by mouth while the intestine heals. In some cases, a baby may need surgery to remove damaged parts of intestine.
  • Retinopathy of prematurity (also called ROP). ROP is an eye disease that affects many premature babies. ROP happens when a baby’s retinas don’t fully develop in the weeks after birth. The retina is the nerve tissue that lines the back of the eye. ROP usually affects both eyes. If your baby has ROP, getting treatment right away is really important. The disease can develop very quickly and take away your baby’s vision if it’s not checked carefully by his doctor at recommended checkups after he leaves the hospital. Some babies need treatment with medicine or laser surgery to prevent vision loss.
  • 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. This happens when the liver isn’t fully developed or isn’t working. Babies with severe jaundice may be treated with light therapy, blood transfusion or intravenous immunoglobulin (also called IVIg). During light therapy, a baby is placed under special lights that help her body change bilirubin into a form she can get rid of in her urine. If this doesn’t work, your baby may get a special type of blood transfusion called an exchange transfusion. During an exchange transfusion new blood is put into your baby’s body to help replace your baby’s blood and get rid of the bilirubin in her blood. If you and your baby have different blood types, your baby may get immunoglobulin (a blood protein) through a needle into a vein. This can help treat jaundice so your baby’s less likely to need an exchange transfusion.
  • Infections. The immune system protects your body from infection. A premature baby’s immune system may not be fully developed, which can lead to infections.

What health conditions may affect a low-birthweight baby later in life?

Babies born with low birthweight may be more likely than babies born at a normal weight to have certain health conditions later in life, including:

  • Diabetes
  • Heart disease
  • High blood pressure
  • Intellectual and developmental disabilities. These are problems with how the brain works that can cause a person to have trouble or delays in physical development, learning, communicating, taking care of himself or getting along with others.
  • Metabolic syndrome. This is caused when you have high blood pressure, diabetes and heart disease all together.
  • Obesity. This means being very overweight. If you're obese, your body mass index (BMI) is 30 or higher. To find out your BMI, go to www.cdc.gov/bmi.

Talk to your baby’s health care provider about what you can do to help your baby be healthy. As your child grows, make sure she eats healthy food, stays active and goes to all her health care checkups. Getting regular checkups throughout childhood 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 she needs to stay protected from certain harmful diseases.

If your baby has developmental delays, does she 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. A developmental milestone is a skill or activity that most children can do at a certain age. Milestones include sitting, walking, talking, having social skills and having thinking skills. 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: March, 2018