One newborn in six weighs less than 2,500 grammes

Nearly 25 million infants were born with low birth weight in 1990, according to information from WHO's Safe Motherhood database. This situation is virtually unchanged since the late 1970s when the first estimates were produced. WHO defines low birth weight as weight at birth of less than 2500 gm whatever the gestational age. It is normally caused by either prematurity (birth at less than 37 weeks) or retarded growth in the uterus, or a combination of the two. Low birth weight is most likely to occur in developing countries. Low birth weight babies account for 17% of the world's live births, according to WHO. The region with the highest incidence is Asia where 21% of babies have low birth weight. In Oceania, 20% of babies have low birth weight, followed by Africa (15%). Latin America (11%), North America (7%) and Europe (6%). In southern Asia, where almost a third of the world's births take place, 1 in 3 live newborns have low birth weight. Infants with low birth weight, especially in developing countries, have a higher risk of being malnourished by the time they are 1 year old. By the age of 4 or 5 they have a higher risk of both malnutrition and infection which impairs their growth further. Poor intrauterine growth is most likely when the mother has low calorie intake or low weight gain, if she had low weight before pregnancy, is short of stature, smokes cigarettes, or has malaria. Cigarette smoking and low birth weight of the mother may contribute to premature birth, but the main causes of prematurity are reproductive trace infections and sexually transmitted diseases.