Low birthweight thus defines a heterogeneous group of infants: some are born early, some are
born growth restricted, and others are born both early and growth restricted. It is generally recognized that being born with low birthweight is a disadvantage for the baby.
For industrialized countries, the main sources of information on low birthweight are service-based
data and national birth registration systems. For developing countries, low birthweight estimates are primarily derived from national household surveys, as well as data from routine reporting systems. The data used
in this report were published by June 2004; reported data generally referred to the period 1997–2001.