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Reproductive and Birth Outcomes

Low Birthweight and the Environment

Birth weight is the first weight of the newborn measured immediately after birth. Birth weight of less than 5.5 lbs, or 2500 grams, is considered low birth weight. A low birth weight infant can be born too small, too early, or both. This can happen for many different reasons which may or may not be related. For example, smoking during pregnancy is associated with infants born too small (growth retardation) than too early (prematurity). For this reason, low birth weight information on the Tracking Network includes only infants who are born full-term.

A doctor taking food print of a newborn baby

Compared to infants of normal weight, low birth weight infants may be more at risk for many health problems. Some babies may become sick in the first six days of life (perinatal morbidity) or develop infections. Other babies may even suffer from longer-term problems such as delayed motor and social development or learning disabilities.

Exposure to lead, solvents, pesticides, polycyclic aromatic hydrocarbons (PAHs), and air pollution during pregnancy has been associated with low birth weight.

Exposure and Risk

A burning cigarette sitting in an ashtray with a pacifier sitting on table next to it.A pregnant woman may increase her chances of having a low birth weight baby if her lifestyle includes any of these risk factors:

  • Smoking,
  • Drinking alcohol,
  • Lack of weight gain,
  • Younger than 15 years and older than 35 years,
  • Social and economic factors:
    • Low income,
    • Low educational level,
    • Stress,
    • Domestic violence or other abuse, and
    • Unmarried.
  • Previous preterm birth, and
  • Exposure to air pollution (both indoor and outdoor) and drinking water contaminated with lead, which are considered environmental risk factors.

Intrauterine (inside the womb) growth retardation can be caused if a pregnant woman:

  • Smokes, or
  • Does not gain enough weight during pregnancy.


Early and regular prenatal care helps identify conditions and behavior that can result in low birth weight infants. Some factors that can cause problems include: smoking, drug and alcohol abuse, lack of weight gain during pregnancy, and pregnancy again within six months or less. Infants born to teenage mothers have a higher risk of being low birth weight babies and a higher mortality rate. To reduce the risk of having a low-birth weight infant, a woman can:

A woman wearing orange breaking a cigarette in half.
  • Quit smoking,
  • See a doctor for a medical checkup before pregnancy,
  • Work with a health care provider to control diseases such as high blood pressure or diabetes,
  • Get preconception health care and early prenatal care and throughout the pregnancy,
  • Discuss concerns during pregnancy with a doctor, and seek medical attention for any warning signs or symptoms of preterm labor, and
  • Take a daily multivitamin containing 400 micrograms of folic acid before and throughout pregnancy.

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