As defined as World Health Organization (WHO), low birthweight is a weight at birth less than 2,500 grams (5.5 pounds). Infants weighing less than 2,500 g are approximately 20 times more likely to die than the babies more than 2500g. A birthweight below 2,500 g contributes to a range of poor health outcomes. A baby’s low weight at birth is either the result of preterm birth (before 37 weeks of gestation) or due to restricted foetal (intrauterine) growth.

The goal of reducing low birthweight incidence by at least one third between 2000 and 2010 is one of the major goals in ‘A World Fit for Children’, – the Declaration and Plan of Action adopted by the United Nations General Assembly Special Session on Children in 2002. The reduction of low birthweight is an important indicator for monitoring progress towards the Millennium Development Goal (MDG) for reducing child mortality. Low birthweight is closely associated with foetal and neonatal mortality and morbidity, inhibited growth and cognitive development, and chronic diseases later in life.

Many factors affect the duration of gestation and foetal growth, and thus, the birthweight. They relate to the infant, the mother, or the physical environment and play an important role in determining the birthweight and the future health of the infant.

Birthweight is affected to a great extent by the mother’s own foetal growth and her diet from birth to pregnancy, and thus, her body composition at conception. Mothers in deprived socio-economic conditions frequently have low birthweight infants. In those settings, the infant’s low birthweight stems primarily from the mother’s poor nutrition and health over a long period of time, including during pregnancy, the high prevalence of specific and non-specific infections, or from pregnancy complications, underpinned by poverty. Physically demanding work during pregnancy also contributes to poor foetal growth.

More than 20 million infants worldwide, representing 15.5 per cent of all births, are born with low birthweight, 95.6 per cent of them in developing countries. The level of low birthweight in developing countries (16.5 per cent) is more than double the level in developed regions (7 per cent).

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.

Excerpt from: Low Birthweight: Country, regional and global estimates – 2004