Low Birth Weight (LBW)

The  United  States  is  unsurpassed  in  its  ability to rescue the very smallest infants; infants who weigh only 750 g at birth are now surviving. However, these rescue efforts are often associated with significant long-term health and developmental problems among survivors.  In  1950,  the World  Health  Organization adopted the figure of less than 2,500 g (5 lb, 8 oz) as a universal definition of low birth weight (LBW). Below that, two subgroups are very low birth weight (VLBW—1,500 g; <3 lb) and extremely low birth weight (750 g; 1 lb, 10 oz). In the United States, the LBW rate of 7.6% in 2000 was twice that of other developed nations, and it has not improved. As a result, LBW has become a public health concern focusing on its impact on infant mortality.

Terminology: Premature Versus Small For Gestational Age

LBW infants are also classified according to whether they are preterm or small for gestational age (SGA). Preterm delivery is the most accurate term to use  in  describing  babies  born  chronologically  too soon, and is defined as a live-born infant born before the end of the 37th week of gestation (compared with full-term gestation of 40–42 weeks). For many years, LBW and prematurity were essentially synonymous.

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In contrast, infants who are SGA are those whose birth weight is below normal when the length of the pregnancy is considered. They may be preterm or full term, and they weigh less than 90% of all babies of the same gestational age. Inadequate nutrition and smoking are among the main factors in producing SGA infants.

Neonatal Intensive Care Unit

The development and availability of neonatal intensive care have saved the lives of many LBW infants. Technological and pharmacological improvements during the 1970s and 1980s included fetal monitors, cesarean delivery, neonatal monitoring of heart rate, respiration and blood pressure, intravenous nutrition, phototherapy to treat jaundice, and drugs to treat apnea and heart conditions. Currently, federal child abuse regulations mandate care for all live-born infants unless the infant is irreversibly comatose or is in a condition in which treatment would be “virtually futile” and inhumane by prolonging death. Ethical questions arise for health care providers, families, and society when they must decide if an infant is so sick that neonatal intensive care should be stopped. The probability of survival, pain and suffering, future quality of life, and the economic cost of care must be considered in the care for the very smallest infants.


In the United States, there has been an increase in the number of LBW infants in the past two decades (from 6.8 per 1,000 in 1980 to 7.8 per 1,000 in 2002), in part due to the increasing number of adolescents having babies, drug abuse, and poor nutrition. Race differences are also apparent. In 2002, the LBW rate for white infants was 6.8%, compared with 13.3% for black infants. Despite the fact that black infants constitute 17% of all births, 33% of all LBW births, and 38% of all VLBW births, black infants are more than twice as likely as white infants in the United States to be born before 37 weeks’ gestation. Race differences are not entirely explained by ethnic differences in the occurrence of various health conditions or behaviors (e.g., smoking, drug use, lack of prenatal care).

Causes And Risk Factors

Very little is known about the absolute causes of LBW and preterm birth despite the extensive amount of research. LBW that results from poor fetal growth is associated with cigarette smoking, low maternal weight gain, and low prepregnancy weight. These account for nearly two thirds of all growth-retarded infants. Other risk factors are black race, first birth, prior LBW birth, maternal illness, fetal infections, and a variety of metabolic and genetic disorders. Although many of these risk factors provide important clues about the causes of LBW, many of them are only weakly related to LBW and are generally not modifiable by intervention programs or changes in public policy. Even less is known about the risk factors for early delivery.

Social Disadvantage And Lifestyle Issues

LBW is the primary biological link in the relationship between socioeconomic status and infant mortality in industrialized countries. Researchers have found that virtually all of the indicators of parents’ social position (occupation, education, achievement, income, marital status) impact the birth weight distribution. In addition to sociodemographic factors that affect birth outcomes, lifestyle issues also contribute, such as mother’s nutrition (weight gain, diet, and nutrient intake); health choices (smoking, alcohol, caffeine, drugs); stress and physical activities; social support; experience of violence; and sexually transmitted diseases. Sadly, this fosters the belief that women are solely to blame for their undesirable behaviors without acknowledging the lack of support from the health care system and society.


The number of children born and surviving LBW has increased, and in parallel, medical technology has continued to improve, and the number of services for LBW children has continued to increase. These advancements come with a price. LBW infants make up 7% of all infants, but 35% of the dollars spent on health care designated for infants goes toward their care, with nearly half of these dollars going toward the care of the tiniest infants. Hospital bills for rescuing only one of these tiny babies can reach more than 1 million dollars. Initial hospitalization costs associated with LBW include physician fees and an average hospital stay of 3 to 4 months, much of which is spent on life-support equipment. Rehospitalization costs during the first year of life and long-term support services (e.g., institutional care, special education) also contribute to the high cost of surviving LBW babies. The extra time that parents of sick LBW babies devote to their care is another component of cost not typically factored in.

LBW children do not necessarily outgrow many of their health problems as they mature. For those who survive infancy with chronic health problems, use of inpatient and outpatient health care services may remain high and access to specialized developmental services may become important. In comparison with normal birth weight children, LBW preschoolers are twice as likely to be hospitalized, and they spend more time in the hospital once admitted. They are also 50% more likely to be enrolled in special education programs, more likely to miss school days because of illness, and more likely to repeat grades in school.

Prevention And Treatment

From a public health perspective, two major strategies to reduce the number of infant deaths in the United States are to (1) prevent LBW and preterm delivery, and (2) improve the survival of LBW infants. Where available, prevention and enrichment programs have been effective in servicing families with LBW children. A relatively simple recommendation for prevention involves smoking cessation; up to 20% of all LBW births could be prevented if no pregnant woman smoked cigarettes. The most common public health recommendations for preventing LBW and preterm births include developing women’s health programs that include prepregnancy counseling, and providing health care resources and insurance coverage devoted to prenatal smoking cessation programs.

If preventive actions are not taken, intervention programs may be accessed. Many early hospital-based interventions incorporate human touch, or massage, which has been proven to improve infant activity levels, alertness, and performance on developmental tests. Several neonatal programs include infant educational enrichment in combination with parent support programs. Intensive enrichment programs that provide medical, educational, and social support services for the parents and child have been shown to improve short-term developmental outcomes for LBW children. Infants who benefit the most from these programs have mothers who have high school or less than high school education levels.

Developmental Consequences

Survival and Risks

The increase in the rate of survival for LBW infants is so large that it is now having an impact on the childhood population. Most infants born at 24 or more weeks of gestational age (GA) survive. For infants born before 24 weeks’ GA, 10% to 40% survive, and at 22 weeks’ GA, almost no infants survive. The risk for severe handicap in VLBW survivors (e.g., cerebral palsy, epilepsy, or blindness) is about 20%, and of the nonhandicapped remainder, at least one third will experience substantial school difficulties. Medical and biological factors that contribute to the risk associated with LBW include birth defects, male sex, birth asphyxia, and neonatal complications including severe brain damage, chronic lung disease, meningitis, seizures, hypoglycemia, and jaundice.

A different picture emerges for moderately LBW groups who do not require intensive care; this group has not been well studied. Most moderately LBW children function within the normal range, yet when compared with normal birth weight children, LBW children have higher rates of mental retardation, cerebral palsy, blindness, deafness, psychomotor problems, school failure, and subnormal growth health problems. The number and severity of these problems increase as birth weight decreases.


Depending on the severity of health problems, LBW children may experience combinations of various health,  neurosensory,  and  developmental  problems that can worsen clinical and educational outcomes. LBW children experience more physical and health problems than children with normal birth weights, beginning  with  lower  average  weight,  height,  and head circumference. Poor health outcomes increase as birth weight decreases, including asthma, upper and lower respiratory infections, and ear infections. Rehospitalizations for medical conditions and surgeries may be needed for the eyes, ears, nose, and throat; orthopedic surgery may also be warranted for cerebral palsy.

Cerebral palsy is the most common major neurological abnormality seen in LBW children, and cognitively, these children score significantly lower on intelligence tests than do children of normal birth weight, even when sociodemographic risk factors are taken into account.

Evaluations may reveal problems with specific cognitive functions, such as language abilities, memory, attention, fine and gross motor coordination, perceptual-motor skills, and nonverbal reasoning and problem solving. By school age, LBW children are more likely than those with normal birth weights to have a learning disability or attention deficit disorders.

In addition to the various health outcomes possible for LBW children, social and environmental factors can worsen long-term outcomes. For example, the combination of severe neonatal illness and a deprived environment that can barely meet basic food and shelter needs can be devastating. Impoverished environments may also include elements of neglect ranging from exposure to environmental hazards to financial devastation to abuse.

Policy Implications

Fortunately, public laws have come into place, and this reflects the importance of early intervention services for infants born LBW. Public Law 94-142, passed in 1975, mandated services for disabled children 6 years of age and older. Part B of Public Law 99-457, passed in 1986, mandated services for disabled children 3 to 5 years of age, and Part H of this legislation created a family-based service model for children from birth to 2 years. In addition to these policies, public health recommendations call for provisions to prevent prematurity as part of prenatal care and mandate comprehensive follow-up of LBW children until school age. Such a mandate would include referral to early intervention services for those most in need and offering parent support and education programs to enable parents to meet the complex needs of preterm children.


  1. Hack, , Klein, N. K., & Taylor, H. G. (1995). Long-term developmental outcomes of low birth weight infants. The Future of Children, 5(1), 176–196.
  2. March of Dimes, http://www.modimes.org
  3. Parents of Premature Babies, http://www.Preemie-L.org
  4. Rossetti, L. (1989). High-risk infants: Identification, assessment and Boston: College Hill Press.
  5. Widerstrom, H., Mowder, B. A., & Sandall, S. R. (1991). At-risk and handicapped newborns and infants. Development, assessment and intervention. Englewood Cliffs, NJ: Prentice-Hall.