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Very Low Birthweight

What is very low birthweight?

Very low birthweight 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 birthweight babies in the US 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 birthweight look much smaller than other babies of normal birthweight. A very low birthweight baby's head 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.

Statistics for very low birthweight

Consider the latest available statistics from the National Center for Health Statistics:


Percentage of Total Births

less than 2,500 grams (5.5 lbs)

6.4 percent

1,500 to 1,999 grams (3.3 to 4.4 lbs)

1.6 percent

What causes very low birthweight?

The primary cause of very low birthweight is preterm birth (born before 37 weeks gestation). Very low birthweight 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 birthweight 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 birthweight babies who have IUGR are also born early, and are both very small and physically immature.

Who is affected by very low birthweight?

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 birthweight. These include:

  • Race
    African-American babies are twice as likely to have very low birthweight than Caucasian babies.

  • Age
    Teen mothers (especially those younger than 15 years old) have a much higher risk of having a baby with very low birthweight.

  • Multiple birth
    Multiple birth babies are at increased risk of very low birthweight because they often are premature. About 10 percent of twins and more than one-third of triplets have very low birthweight.

  • Mother's health
    Women who are exposed to drugs, alcohol, and cigarettes during pregnancy are more likely to have low or very low birthweight 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 birthweight.

Why is very low birthweight a concern?

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

Because many babies with very low birthweight 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 birthweight the greater the risks for complications. The following are some of the common problems of very low birthweight babies:

  • Low oxygen levels at birth

  • Inability to maintain body temperature

  • Difficulty feeding and gaining weight

  • Infection

  • Breathing problems, such as 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) - a serious disease of the intestine common in premature babies.

  • Sudden infant death syndrome (SIDS)

Nearly all very low birthweight 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 birthweight. Generally, the lower the birthweight, the greater the chances for developing intellectual and neurological problems, which may include the following:

  • Cerebral palsy

  • Blindness

  • Deafness

  • Mental retardation

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

How is very low birthweight diagnosed?

During pregnancy, a baby's birthweight 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 birthweight less than 2,500 grams (5 pounds, 8 ounces) is diagnosed as low birthweight. Babies weighing less than 1,500 grams (3 pounds, 4 ounces) at birth are considered very low birthweight.

Treatment for very low birthweight

Specific treatment for very low birthweight 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 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

  • Other treatments for complications

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

Prevention of very low birthweight

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 birthweight.

Prenatal care is a key factor in preventing preterm births and very low birthweight 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 birthweight, 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, SIDS, and other complications.

To request an appointment with a physician at St. Louis Children's Hospital, call 314.454.5437 or 800.678.5437 or email us.  For additional resources about very low birthrate, contact our Family Resource Center.