Low birthweight in newborns

  • 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 5 pounds, 8 ounces is diagnosed as low birthweight. Babies weighing less than 3 pounds, 5 ounces at birth are considered very low birthweight.

    • The average newborn weighs about 7.6 pounds

    • About 7.6 percent of all newborns in the United States have low birthweight.

    • The overall rate of these very small babies is increasing, primarily because of the increase in multiple birth babies, who tend to be born earlier and weigh less. More  than half of multiple birth babies have low birthweight.

    How Boston Children's Hospital approaches very low birthweight

    The Infant Follow-Up Program is designed for infants born very prematurely, who weigh less than 3.3 lbs and are at high risk for development and motor delays and other problems resulting from prematurity. Our program follows children from the time of discharge until they reach age 3 to 4.

    The multi-disciplinary Infant Follow-Up team includes pediatricians, neonatologists, pediatric psychologists, physical therapists, social workers and if needed, pediatric neurologists.

    Contact Us

    Infant Follow-Up Program
    Boston Children's Hospital Boston
    300 Longwood Avenue
    Fegan 10
    Boston MA 02115

    617-355-6622
    fax: 617-730-0252

  • What causes low birthweight?

    The primary cause is premature birth, being born before 37 weeks gestation; a baby born early has less time in the mother's uterus to grow and gain weight, and much of a fetus's weight is gained during the latter part of the mother's pregnancy.

    Another cause of low birthweight is intrauterine growth restriction. This occurs when a baby does not grow well in utero because of problems with the placenta, the mother's health or birth defects. Babies with Intrauterine growth restriction (IUGR) may be born early or full-term; premature babies with IUGR may be very small and physically immature, and full-term babies with IUGR may be physically mature but weak.

    Which babies are affected by low birthweight?

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

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

    • Mother's age - Teen mothers (especially those younger than 15) have a much higher risk of having a baby with low birthweight.

    • Multiple birth - Multiple birth babies are at increased risk of low birthweight because they often are premature.

    • 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.

    Why is low birthweight a concern?

    If your baby has a low birthweight, she may be at increased risk for complications. Her tiny body is not as strong, and she may have a harder time eating, gaining weight and fighting infections. Because she has so little body fat, she may have a hard time staying warm in normal temperatures.

    Because many babies with low birthweight 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 a baby's birthweight, the greater the risks for complications. The following are some of the common problems of low birthweight babies:

    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. Fortunately, there is a 95 percent chance of survival for babies weighing between 3 pounds, 5 ounces and 5 pounds, 8 ounces.

    Can low birthweight be prevented?

    Prevention of preterm births is one of the best ways to prevent babies born with low birthweight. Prenatal care is a key factor in preventing preterm births and low birthweight 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 birthweight, eating a healthy diet and gaining the proper amount of weight in pregnancy are essential.

    • Mothers should avoid alcohol, cigarettes and illicit drugs, which can contribute to poor fetal growth, among other complications.

  • 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 5 pounds, 8 ounces is diagnosed as low birthweight. Babies weighing less than 3 pounds, 5 ounces at birth are considered very low birthweight

  • Care for low birthweight babies may include:

    • 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

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

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- Sandra L. Fenwick, President and CEO
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