Low birth weight

Low birth weight is a term used to describe babies who are born weighing less than 2,500 grams (5 pounds, 8 ounces). In contrast, the average newborn weighs about 8 pounds. A low birth weight baby can be born too small, too early (premature), or both. This can happen for many different reasons. They include health problems in the mother, genetic factors, problems with the placenta and substance abuse by the mother.

Over 8 percent of all newborn babies in the United States have low birth weight. The overall rate of these very small babies in the United States is increasing. This is primarily due to the greater numbers of multiple birth babies who are more likely to be born early and weigh less. Over half of multiple birth babies have low birthweight compared with only about 6 percent of single birth babies.

Babies with low birth weight look much smaller than other babies of normal birth weight. A low birthweight baby’s head may appear to be bigger than the rest of the body, and he or she often looks thin with little body fat. Some babies with low birth weight are healthy, even though they’re small. But being low birth weight can cause serious health problems for some babies. A baby with low birth weight may have trouble eating, gaining weight and fighting off infections. Some low-birth weight babies may have long-term health problems, too.

Some low birth weight babies may be more at risk for certain health problems. Some may become sick in the first days of life or develop infections. Others may suffer from longer-term problems such as delayed motor and social development or learning disabilities.

The primary cause of low birthweight is premature birth (being born before 37 weeks gestation). Being born early means a baby has less time in the mother’s uterus to grow and gain weight. Much of a baby’s weight is gained during the latter part of pregnancy.

Another cause of low birthweight is intrauterine growth restriction (IUGR). This occurs when a baby does not grow well during pregnancy because of problems with the placenta, the mother’s health, or the baby’s condition. A baby can have IUGR and be born at full term (37 to 41 weeks). Babies with intrauterine growth restriction (IUGR) born at term may be physically mature but may be weak. Premature babies that have intrauterine growth restriction (IUGR) are both very small and physically immature.

Low birth weight key points

Low birth weight is when a baby is born weighing less than 5 pounds, 8 ounces.
Some low-birth weight babies are healthy, but others have serious health problems that need treatment.
About 1 in 12 babies (about 8 percent) in the United States is born with low birth weight.
Premature birth (before 37 weeks of pregnancy) and fetal growth restriction are the most common causes of low birth weight.
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 healthcare provider about what you can do to help reduce your risk for having a baby with low birth weight.

What is very low birth weight

Very low birth weight is a term used to describe babies who are born weighing less than 1,500 grams (3 pounds, 4 ounces). Only a few babies, 1.5 percent, are born this tiny. However, the overall rate of very low birth weight babies in the U.S. is increasing. This is primarily due to the greater numbers of multiple birth babies who are more likely to be born early and weigh less.

Babies with very low birth weight look much smaller than other babies of normal birth weight. A very low birth weight baby’s head usually appears to be bigger than the rest of the body and he or she often looks extremely thin, with little body fat. The skin is often quite transparent, allowing the blood vessels to be easily seen.

Table 1. Statistics for very low birthweight from the National Center for Health Statistics for 2011

Birth weight	Percentage of total births
less than 2,500 grams (5.5 lbs.)	8.1 percent
less than 1,500 grams (3.3 lbs.)	1.4 percent

What causes very low birth weight?

The primary cause of very low birth weight is preterm birth (born before 37 weeks gestation). Very low birth weight babies are often born before 30 weeks of pregnancy. Being born early means a baby has less time in the mother’s uterus to grow and gain weight. Much of a baby’s weight is gained during the latter part of pregnancy.

Another cause of very low birth weight is intrauterine growth restriction (IUGR). This is when a baby does not grow well during pregnancy because of problems with the placenta, the mother’s health, or birth defects. Most very low birth weight babies who have intrauterine growth restriction (IUGR) are also born early, and are both very small and physically immature.

Who is affected by very low birth weight?

Any baby born early is more likely to be very small. However, there are other factors that can also contribute to the risk of very low birth weight. These include:

Race. African-American babies are twice as likely to have very low birth weight than white babies.
Age. Mothers who are younger than age 17 or older than age 35 have a much higher risk of having a baby with very low birth weight.
Multiple birth. Multiple birth babies are at increased risk of very low birth weight because they often are premature. About 10 percent of twins and more than one-third of triplets have very low birth weight.
Mother’s health. Women who are exposed to drugs, alcohol, and cigarettes during pregnancy are more likely to have low or very low birth weight babies. Mothers of lower socioeconomic status are also more likely to have poorer pregnancy nutrition, inadequate prenatal care, and pregnancy complications–all factors that can contribute to very low birth weight.

Very low birth weight prevention

Because of the tremendous advances in care of sick and premature babies, more and more babies are surviving despite being born early and being born very small. However, prevention of preterm births is one of the best ways to prevent very low birth weight.

Prenatal care is a key factor in preventing preterm births and very low birth weight babies, as well as in reducing the risk for SIDS. At prenatal visits, the health of both mother and fetus can be checked. Because maternal nutrition and weight gain are linked with fetal weight gain and birth weight, eating a healthy diet and gaining the proper amount of weight in pregnancy are essential. Mothers should also avoid alcohol, cigarettes, and illicit drugs, which can contribute to poor fetal growth, sudden infant death syndrome (SIDS), and other complications.

Very low birth weight effects

A baby with very low birth weight is often at increased risk for complications. The baby’s tiny body is not as strong and he or she may have a harder time eating, gaining weight, and fighting infection. Because they have so little body fat, very low birth weight babies often have difficulty staying warm in normal temperatures.

Because many babies with very low birth weight are also premature, it can be difficult to separate the problems due to the prematurity from the problems of just being so tiny. In general, the lower the baby’s birth weight the greater the risks for complications. The following are some of the common problems of very low birth weight babies:

Low oxygen levels at birth
Inability to maintain body temperature
Difficulty feeding and gaining weight
Infection
Breathing problems, such as infant respiratory distress syndrome (a respiratory disease of prematurity caused by immature lungs)
Neurological problems, such as intraventricular hemorrhage (bleeding inside the brain)
Gastrointestinal problems, such as necrotizing enterocolitis (NEC). This is a serious disease of the intestine common in premature babies.
Sudden infant death syndrome (SIDS)

Nearly all very low birth weight babies need specialized care in the Neonatal Intensive Care Unit (NICU) until they can gain weight and are well enough to go home.

Generally, the smaller the baby, the higher the risk. The survival of these tiny babies is directly related to their weight at birth.

Risks for long-term complications and disability are increased for babies with very low birth weight. Generally, the lower the birth weight, the greater the chances for developing intellectual and neurological problems, which may include the following:

Cerebral palsy
Blindness
Deafness
Developmental delay

Consult your baby’s doctor for information about your baby’s risks.

How is very low birth weight diagnosed?

During pregnancy, a baby’s birth weight can be estimated in different ways. The height of the fundus (the top of a mother’s uterus) can be measured from the pubic bone. This measurement in centimeters usually corresponds with the number of weeks of pregnancy after the 20th week. If the measurement is low for the number of weeks, the baby may be smaller than expected. Ultrasound (a test using sound waves to create a picture of internal structures) is a more accurate method of estimating fetal size. Measurements can be taken of the fetus’ head and abdomen and compared with a growth chart to estimate fetal weight.

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. A birth weight less than 2,500 grams (5 pounds, 8 ounces) is diagnosed as low birth weight. Babies weighing less than 1,500 grams (3 pounds, 4 ounces) at birth are considered very low birth weight.

Very low birth weight treatment

Specific treatment for very low birth weight will be determined by your baby’s doctor based on:

Your baby’s gestational age, overall health, and medical history
Your baby’s tolerance for specific medications, procedures, or therapies
Your opinion or preference

Care for very low birth weight babies often includes:

Care in the NICU
Temperature controlled beds
Special feedings, sometimes with a tube into the stomach if a baby cannot suck
Other treatments for complications

Very low birth weight babies may have a harder time “catching up” in physical growth because they often have other complications. Many very low birth weight babies are referred to special follow-up healthcare programs.

What causes low birth weight

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

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 birth weight 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.
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 birth weight simply because their parents are small. Others may have low birth weight 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 birth weight. Babies with birth defects are more likely than babies without birth defects to be born prematurely.

Who is affected by low birth weight?

Any baby born prematurely is more likely to be very small. However, there are other factors that can also contribute to the risk of very low birth weight. These include:

Race. African-American babies are two times more likely to have low birthweight than white babies.
Age. Teen mothers (especially those younger than 15 years old) have a much higher risk of having a baby with low birthweight.
Multiple birth. Multiple birth babies are at increased risk for low birthweight because they often are premature. Over half of twins and other multiples have low birthweight.
Mother’s health. Babies of mothers who are exposed to illicit drugs, alcohol, and cigarettes are more likely to have low birthweight. Mothers of lower socioeconomic status are also more likely to have poorer pregnancy nutrition, inadequate prenatal care, and pregnancy complications–all factors that can contribute to low birthweight.

Are you at risk of having a low-birth weight baby?

Scientists know some things may make you more likely than others to have a low-birth weight baby. These are called risk factors. Having a risk factor doesn’t mean for sure that you’ll have a low-birth weight baby. But it may increase your chances. Because many premature babies are born with low birth weight, many risk factors for preterm labor and premature birth are the same as for having a low-birth weight baby. Talk to your health care provider about what you can do to help reduce your risk.

Medical risk factors for having a low-birth weight 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 birth weight 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-birth weight 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 birth weight.

Risk factors in your everyday life for having a low-birth weight 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 small for gestational age (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. Low socioeconomic status 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-birth weight 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-birth weight baby. In the United States, black women are more likely than others to have a low-birth weight baby. The rates of babies born with low birth weight 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)

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

Low birth weight prevention

Prenatal care is a key factor in preventing preterm births and low birth weight babies. At prenatal visits, the health of both mother and fetus can be checked. Because maternal nutrition and weight gain are linked with fetal weight gain and birth weight, eating a healthy diet and gaining the proper amount of weight in pregnancy are essential. Mothers should also avoid alcohol, cigarettes, and illicit drugs, which can contribute to poor fetal growth, among other complications.

Low birth weight effects

A baby with low birth weight may be at increased risk for complications. The baby’s tiny body is not as strong and he or she may have a harder time eating, gaining weight, and fighting infection. Because they have so little body fat, low birth weight babies often have difficulty staying warm in normal temperatures.

Because many babies with low birth weight are also premature, it is can be difficult to separate the problems due to the prematurity from the problems of just being so tiny. In general, the lower the birth weight, the greater the risk for complications. The following are some of the common problems of low birth weight babies:

Low oxygen levels at birth
Inability to maintain body temperature
Difficulty feeding and gaining weight
Infection
Breathing problems, such as infant respiratory distress syndrome (a respiratory disease of prematurity caused by immature lungs)
Neurologic problems, such as intraventricular hemorrhage (bleeding inside the brain)
Gastrointestinal problems, such as necrotizing enterocolitis (a serious disease of the intestine common in premature babies)
Sudden infant death syndrome (SIDS)

Nearly all low birth weight babies need specialized care in the Neonatal Intensive Care Unit (NICU) until they gain weight and are well enough to go home. Survival of infants with low birth weight depends largely on how much the baby weighs at birth, with the smallest babies (<500 grams) having the lowest survival rate.

What is low birth weight is a known risk factor for?

Low-birth weight 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. Babies with respiratory distress syndrome 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 respiratory distress syndrome 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). Patent ductus arteriosus 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 patent ductus arteriosus, 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. Necrotizing enterocolitis can be dangerous for a baby leading to feeding problems, swelling in the belly and other complications. Babies with necrotizing enterocolitis 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. Retinopathy of prematurity is an eye disease that affects many premature babies. Retinopathy of prematurity 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. Retinopathy of prematurity usually affects both eyes. If your baby has retinopathy of prematurity, 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-birth weight baby later in life?

Babies born with low birth weight 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.

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.

How is low birth weight diagnosed?

During pregnancy, a baby’s birth weight can be estimated in different ways. The height of the fundus (the top of a mother’s uterus) can be measured from the pubic bone. This measurement in centimeters usually corresponds with the number of weeks of pregnancy after the 20th week. If the measurement is low for the number of weeks, the baby may be smaller than expected. Ultrasound (a test using sound waves to create a picture of internal structures) is a more accurate method of estimating fetal size. Measurements can be taken of the fetus’ head, abdomen, and femur and compared with a growth chart to estimate fetal weight.

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. A birth weight less than 2,500 grams (5 pounds, 8 ounces) is diagnosed as low birth weight. Babies weighing less than 1,500 grams (3 pounds, 5 ounces) at birth are considered very low birth weight.

Low birth weight treatment

Specific management for low birth weight will be determined by your baby’s doctor based on:

Your baby’s gestational age, overall health, and medical history
Your baby’s tolerance for specific medications, procedures, or therapies
Your opinion or preference

Care for low birth weight babies often includes:

Care in the NICU
Temperature controlled beds
Special feedings, sometimes with a tube into the stomach if a baby cannot suck, or through an intravenous (IV) line
Other treatments for complications

Low birth weight babies typically “catch up” in physical growth if there are no other complications. Babies may be referred to special follow-up healthcare programs.

If my 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 (https://www.cdc.gov/ncbddd/actearly/) 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.

Low birth weight