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Last update: Feb 2013

World Fit For Children Goal
To reduce the rate of low birthweight by at least one third


Normal birthweight is critical to future health and development

Birthweight is a strong indicator not only of a birth mother's health and nutritional status but also a newborn's chances for survival, growth, long-term health and psychosocial development.

A low birthweight (less than 2,500 grams) raises grave health risks for children. Low birthweight is a public health problem in many countries; globally an estimated 15 per cent of births result in low-birthweight babies. Babies who are undernourished in the womb face a greatly increased risk of dying during their early months and years. Those who survive have impaired immune function and increased risk of disease; they are likely to remain undernourished, with reduced muscle strength, throughout their lives, and to suffer a higher incidence of diabetes and heart disease. Children born underweight also tend to have cognitive disabilities and a lower IQ, affecting their performance in school and their job opportunities as adults.

Low birthweight can arise as a result of a baby being born too soon (at less than 37 weeks, also known as preterm birth) and/or being born too small for gestational age (small as a result of intrauterine growth restriction). Babies that are born prematurely and are also small for their gestational age have the worst prognosis.

Low birthweight stems primarily from poor maternal health and nutrition. Three factors have most impact: poor maternal nutritional status before conception, short stature (due mostly to undernutrition and infections during childhood) and poor nutrition during pregnancy.

Insufficient antenatal weight gain in particular is a principal cause of foetal growth retardation. Teenagers who give birth when their own bodies have yet to finish growing also have a greater risk of bearing underweight babies. Moreover, maternal diseases such as malaria can significantly impair foetal growth. In addition, a heavy physical workload during pregnancy may also negatively affect birthweight.

Key interventions to prevent low birthweight, therefore, include improved food intake, micronutrient supplementation, preventing and treating diseases such as malaria and HIV/AIDS, educating girls and expectant mothers, and preventing teenage pregnancies.

Challenges in estimating low-birthweight incidence

More than half of newborns globally are not weighed; in South Asia, which has the highest incidence of low-birthweight babies, two out of three newborns are not weighed. Those newborns who are weighed, meanwhile, are generally better off (more likely to be born in health facilities, urban areas and of better-educated mothers), which can lead to an underestimation of the incidence of low birthweight. In addition, when infants are weighed at birth, the readings tend to cluster around multiples of 100 grams. As a result, a certain proportion of infants whose birthweights are reported as exactly 2,500 grams actually weigh less than 2,500 grams. This would further underestimate the incidence of low birthweight.

UNICEF and the World Health Organization (WHO) have adjusted the under-reporting and misreporting of birthweights with results from household surveys (Multiple Indicator Cluster Surveys and Demographic and Health Surveys).

While improving unadjusted statistics, these rates may still underestimate the magnitude of the problem. It is critical, therefore, that all babies be properly weighed at birth.


UNICEF/WHO, Low Birthweight: Country, regional and global estimates, UNICEF, New York, 2004.

'Infant mortality statistics from the 1997 period linked birth/infant death data set' in National Vital Statistics Report, vol. 47, no. 23, 30 July 1999, pp. 1-23.

Barker, D.J. (ed.), Fetal and infant origins of adult disease, BMJ Books, London, 1992.

Monitoring Low Birthweight: An evaluation of international estimates and updated estimation procedure in Bulletin of the World Health Organization, vol. 83, no. 3,  March 2005, pp. 161-240.