The birth weight of an infant is the single most important determinant of its chances of survival and healthy growth and development. Because birth weight is conditioned by the health and nutritional status of the mother, the proportion of infants born with low birth weights (LBW) closely reflects the health status of the communities into which they are born.

LBW has been defined as a birth weight of less than 2,500 g. It can be caused either by premature delivery (short gestation) or by fetal growth retardation. In countries where the proportion of LBW infants is low, most are preterm. In countries where the proportion is high, the majority of LBW infants suffer from fetal growth retardation. The causes of fetal growth retardation are multiple and interrelated and include low maternal food intake, hard physical work during pregnancy, and illness, especially infections. Short maternal stature, very young age, high parity, and close birth spacing are all associated factors.

It is clear from the many causes that there is no single solution to LBW. Interventions have to be cause-specific. Prenatal care, nutrition programs, health education on the needs of pregnant women, family planning, and measures aimed at improving the health and nutrition of young girls all factor in the solution.

At the Thirty-fourth World Health Assembly, the Member States of the World Health Organization (WHO) adopted, as part of the global strategy for health for all by the year 2000, the proportion of infants born with an LBW as one of a number of global indicators with which to monitor progress.

Associated with the use of this indicator, however, are a number of practical problems. In developed countries, most infants are weighed at birth; in developing countries, usually only those born in institutions are weighed. These infants constitute a small--usually privileged--minority. A recent survey has shown that only about one-third of births in the developing world take place in institutions; in some countries, the proportion is lower than one-fifth. Even when records of birth weights exist at the institutional level, they are rarely collated at the national level.

For these reasons, and to obtain an approximate global picture of the availability of data and the extent of the problem of LBW, the Division of Family Health, WHO, Geneva, undertook in 1979 a widespread search of all available sources of information. The results of this search and details of the methodology employed have been published (1). At that time, it was estimated that 21 million LBW infants were born in 1979.

The present review updates that search. A new search, carried out at the end of 1983, yielded some new information on 90 countries, including 20 for which no previous information was available. This brings the total number of countries for which some information is available to 112. The new information was compared to that of the previous search and new estimates made where the data seemed to warrant it.*

Taken as a whole, the data would tend to indicate a slight decrease in the incidence of LBW. It is estimated that, of the 127 million infants born in 1982, 16.0%--some 20 million--had an LBW. This constitutes a decrease in both relative and absolute terms when compared to the estimates for 1979--21 million LBW infants making up 16.8% of the 122 million born that year. For developing countries only, the proportion has fallen from 18.4% to 17.6%.

Variations between and within geographic regions remain considerable and have not greatly changed (Table 1). The incidence of LBW, by region, ranges from 31.1% in Middle South Asia and 19.7% for Asia as a whole to 14.0% in Africa, 10.1% in Latin America, 6.8% in North America, and 6.5% in Europe.

In Africa, the estimated percentage of LBW infants for 1982 is 14.0%, 1% lower than that for 1979. This decrease is largely due to changes in Northern and Southern Africa, where more recent data have changed the estimates for a number of countries, including Egypt and Lesotho. There is no evidence of substantive changes in Eastern and Western Africa, with the possible exception of Kenya which has improved, and Rwanda and the United Republic of Tanzania which have deteriorated. New information is available for a number of countries in these regions, but national rates are all between 10% and 20%. The only change found for Middle Africa was a slight deterioration for Cameroon.

The overall proportion of LBW infants born in Asia has slightly decreased, but in Middle South Asia, where the problem is most acute, there is no evidence of change. Rates in this region remain between 20% and 50%. The marked change in Western South Asia is largely due to new data relating to countries, notably Turkey, for which no information was found previously. The most notable changes in Eastern South Asia are in Singapore (a marked decrease) and Thailand. The estimate for the latter country is based on government data for all institutional births (which comprise 36% of all births). The propotion of LBW infants in East Asia remains very low.

In Latin America, there is evidence of improvement in many countries, with rates in the south approaching those of developed countries. Data from countries whose governments publish national rates--Cuba, Panama, Uruguay, and Venezuela--all show a downward trend.

In Europe as a whole, the incidence of LBW has decreased from 7.7% to 6.5%, although this may be partly an artifact resulting from the availability of better information from Italy. Some improvements are noted in Western and Northern Europe, but very little change took place in countries where the rates were already below 5% in 1979, nor is there any evidence of significant changes in Eastern Europe.

There are slight improvements in the rates for both Canada and the United States. Reported by WHO Weekly Epidemiological Record 1984:59;205-12.

Reference

1. World Health Organization. World Health Statistics Quarterly. 1980;33:197-224. *Details of the studies on which the estimates are based are available from the Division of Family Health, WHO, 1211 Geneva 27, Switzerland.

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