Children's Health and Wellness

Low Birthweight

What is low birthweight?

Low birthweight is a term used to describe babies who are born weighing less than 2,500 grams (5 pounds, 8 ounces). The weight of an average newborn is usually around 8 pounds. Over 8 percent of all newborn babies in the United States have low birthweight, and the number is rising.

Babies with low birthweight look much smaller than other babies of normal birthweight. A low birthweight baby's head may look bigger than the rest of his or her body. He or she often looks thin with little body fat.

What causes low birthweight?

Low birthweight is mostly caused by premature birth (being born before 37 weeks). 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 last weeks of pregnancy.

Another cause of low birthweight is a condition called 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 health. A baby can have IUGR and be born at full term (37 to 41 weeks). Babies with IUGR born at term may be physically mature but may be weak. Premature babies that have IUGR are both very small and physically immature.

There are other things that can also raise the risk of very low birthweight. These include:

  • 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. This is the most common reason for babies to be born with low birthweight.

  • Race. African-American babies are more likely to have a 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.

  • Mother's health. Babies born to mothers who use street drugs, alcohol, and cigarettes are more likely to have low birthweight. Mothers who are considered "low income" are less likely to have good nutrition during pregnancy, less likely to get prenatal care, and more likely to have pregnancy complications. Each of these things can cause low birthweight.

Why is low birthweight a concern?

Low birthweight babies often have problems. The baby's tiny body is not as strong. He or she may have a harder time eating, gaining weight, and fighting infection. Low birthweight babies often have difficulty staying warm in normal temperatures because they don't have much fat on their bodies.

Babies that are born premature often have complications. It is sometimes hard to tell if the problems are a result of being born early, or because they are so small. In general, the lower the birthweight, the greater the risk for complications. The following are some of the common problems of low birthweight babies:

  • Low oxygen levels at birth

  • Difficulty staying warm

  • Difficulty feeding and gaining weight

  • Infection

  • Breathing problems, such as infant respiratory distress syndrome (a problems caused by having immature lungs)

  • Neurologic problems, such as bleeding inside the brain (intraventricular hemorrhage)

  • Gastrointestinal problems (such as necrotizing enterocolitis)

  • Sudden infant death syndrome (SIDS)

Nearly all low birthweight 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 birthweight depends largely on how much the baby weighs at birth. The smallest babies (<500 grams) have the most problems and are less likely to survive. 

How is low birthweight diagnosed?

Your health care provider can check your baby's grown during pregnancy. One way is to measure the distance, or height of the fundus (the top of a mother's uterus) from the pubic bone. This number of centimeters is usually similar to 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. Your health care provider may also use ultrasound to check your baby's growth. Ultrasound is a test that uses sound waves to create a picture of your baby and the inside of your body. It is a more accurate method of checking your baby's size. Measurements can be taken of your baby's head, belly, and upper leg bone. These measurements are compared with a growth chart to estimate his or her 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. If your baby weighs less than 2,500 grams (5 pounds, 8 ounces), he or she has a low birthweight. Babies weighing less than 1,500 grams (3 pounds, 5 ounces) at birth are considered very low birthweight.

Treatment for low birthweight

Specific treatment of low birthweight will be determined by your baby's health care provider 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 birthweight 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 birthweight babies typically "catch up" in physical growth if there are no other complications. Babies may be referred to special follow-up health care programs.

Prevention of low birthweight

More and more babies are surviving despite being born early and being born very small. This is because of the great advances in the care of sick and premature babies. However, prevention of preterm births is one of the best ways to prevent babies born with low birthweight.

Regular prenatal care is the best way to prevent preterm births and low birthweight babies. At prenatal visits, your health and your baby's health are checked. It is important to eat a healthy diet during pregnancy. This will help you to gain enough weight to help your baby grow and to ensure that you stay healthy. Women who are pregnant should not drink alcohol, smoke cigarettes, or use street drugs. All of these can cause low birthweight and other problems for your baby. 

Online Source: Births: Final Data for 2010, CDC
Online Source: PRemature Infant, The Merck Manual for Professionals
Online Editor: Sims, Jane
Online Medical Reviewer: MMI board-certified, academically-affiliated clinician
Online Medical Reviewer: Trevino, Heather M., BSN, RNC
Date Last Reviewed: 9/28/2014
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