Last update:
May 2006
Reduction in the rate of low birth weight by at least one third of the current rate

Low Birthweight - Country, Regional and Global Estimates, UNICEF/WHO 2004

The Challenge

Weight at birth is a good indicator not only of a mother's health and nutritional status but also the newborn's chances for survival, growth, long-term health and psychosocial development. Low birthweight (less than 2,500 grams) carries a range of grave health risks for children. Babies who were 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 suffer a higher incidence of diabetes and heart disease in later life. Children born underweight also tend to have a lower IQ and cognitive disabilities, affecting their performance in school and their job opportunities as adults.

In the developing world, low birthweight stems primarily from the mother's poor health and nutrition. Three factors have most impact: the mother's poor nutritional status before conception, short stature (due mostly to undernutrition and infections during her childhood), and poor nutrition during the pregnancy. Inadequate weight gain during pregnancy is particularly important since it accounts for a large proportion of foetal growth retardation. Moreover, diseases such as diarrhoea and malaria, which are common in many developing countries, can significantly impair foetal growth if the mother becomes infected while pregnant.

In the industrialized world, cigarette smoking during pregnancy is the leading cause of low birthweight. In developed and developing countries alike, teenagers who give birth when their own bodies have yet to finish growing run the risk of bearing underweight babies.

Problems in estimating low birthweight incidence

More than half (58%) of infants
not weighed at birth
Region % of births not weighed
South Asia 74
Sub-Saharan Africa 65
Middle East and North Africa 60
East Asia and Pacific 30
Latin America and Caribbean 17
Developing countries 58
Source: UNICEF/WHO 2004, Low Birth Weight: Country, Regional and Global Estimates.

In developing countries, many infants are not weighed at birth. As a result, much of the available data on low birthweight may not be representative of the population at large; they may be biased toward hospital deliveries and therefore be under-estimates of the true levels.

The large proportion of infants not weighed at birth constitutes a major impediment to reliable monitoring of this important indicator. In the developing world, it is estimated that more than half (58%) of all infants are not weighed at birth. This proportion is highest in South Asia (74%) and Sub-Saharan Africa (65%). Existing data on low birthweight from health service statistics are therefore of limited utility. A major effort is needed to increase the proportion of infants weighed at birth.

UNICEF and WHO publish improved estimates of low birthweight

One of the major challenges in measuring the incidence of low birthweight is the fact that more than half of infants in the developing world are not weighed. In the past, most estimates of low birthweight for developing countries were based on data compiled from health facilities. However, these estimates are biased for most developing countries because the majority of newborns are not delivered in facilities, and those who are represent only a selected sample of all births.

In recent years, household survey data have become much more widely available, and procedures have been applied to these data that adjust for the underreporting and misreporting of birthweights. UNICEF and WHO have recently published a revised set of estimates for low birthweight which include these adjustments and thus represent a major improvement over past assessments. The rates, nonetheless, are still likely to underestimate the true magnitude of the problem.

- UNICEF and WHO, Low Birthweight: Country, Regional and Global Estimates, New York, 2004.
- A. Blanc and T. Wardlaw, 2005, "Monitoring Low Birth Weight: An Evaluation of International Estimates and an Updated Estimation Procedure". WHO Bulletin, 83 (3), 178-185.