Percent of low birth-weight singleton live births, by parity
Low birth weight (LBW) is defined as weight less than 2500 g obtained within 24 hours of birth, regardless of gestational age.
“Live birth” is the the birth of a newborn, irrespective of the duration of gestation, that exhibits any sign of life, such as respiration, heartbeat, umbilical pulsation, or movement of voluntary muscles.
“Parity” is the number of times a woman has given birth.
LBW has two main causes: preterm birth and small-for-gestational age, or intrauterine growth retardation (IUGR). LBW is often used as a proxy indicator to quantify the magnitude of IUGR in developing countries because valid assessment of gestational age is generally not available, so prematurity and IUGR are often not differentiated.
Preterm birth: The term preterm birth is used for infants born before 37-weeks completed gestation. Most, but not all, premature newborns in developing countries weigh less than 2500g.
IUGR: a condition in which fetal growth has been impaired. In developing countries, maternal under-nutrition and maternal ill health including malaria, anemia and acute and chronic infections (e.g., STIs) are major causes.
The numerator and denominator for this indicator are defined according to parity.
For primiparous women, this indicator is calculated as:
Number of LBW singleton live births to women with first birth <2500g x 100
Total number of singleton live births to women with first birth
For multiparous women, this indicator is calculated as:
Number of LBW singleton live births to women with two or more births <2500g x 100
Total number of singleton live births to women with two or more births
Number of newborns with a birth weight less than 2,500g in a defined time period (e.g., 12 months); number of live births in the same time period; parity of the mother.
If targeting and/or linking to inequity, classify sites by location (poor/not poor) and disaggregate newborns by location.
Population-based surveys (i.e. malaria indicator survey, DHS)
Routine health information systems may collect data for this indicator to obtain estimates of LBW for facility births, but facility-based data are not representative, as they are limited to the few women who deliver in facilities. Data from health facilities or delivery records are nevertheless the main
source of data on birth weights obtained during household surveys (Blanc & Wardlaw, 2005). It is therefore critical to ensure that measurement of weight at birth in health facilities is strengthened and routinely recorded on maternity cards and registers.
Approximately 1 in 6 newborns, or 17 million babies, are born every year with LBW. It is the single most important predictor of newborn well-being and survival. Because maternal under-nutrition and malaria-associated maternal anemia are major determinants of LBW, high rates of LBW should be interpreted not only as an indicator of newborn under-nutrition, morbidity, and mortality, but also as an indicator of maternal well being. One of the goals of the World Summit for Children is to reduce the incidence of LBW to less than ten percent (ACC/SCN, 2000a).
In developing countries, approximately two thirds of LBW is caused by IUGR, and the remaining one third is due to preterm birth, although some preterm babies also have IUGR. By contrast, in developed countries, the majority of LBW is due to preterm birth.
LBW babies are ten times more likely to die than babies weighing over 3 kg. They are also more likely to have impaired cognitive development and to develop acute illnesses such as diarrhea and pneumonia in early infancy (ACC/SCN, 2000a).
As the risk for LBW has been shown to be higher among primiparous than mutiparous women, measurement of LBW must be differentiated by parity (WHO, 2007).
Obtaining reliable estimates of LBW in the general population is difficult. In many developing countries, the majority of births occur at home and babies are not weighed. The women surveyed may not know or recall the birth weights of all their children, or they may report them incorrectly. Promoting childbirth in health facilities where infants are weighed at birth is likely to improve the quality of data on birth weight.
Many household surveys collect data on birth weight, but since the weights reported are mainly from facility births, these data are also subject to selection bias. Some household surveys (such as the DHS) ask mothers to state whether their baby was smaller than average or very small; and at an aggregate level these data may be used to estimate incidence of LBW at a national level. Regional estimates are also possible if the sample size is sufficiently large (Boerma et al., 1996).
This indicator measures one of the major objectives of safe pregnancy/neonatal interventions: to prevent LBW. However, since LBW is due to many complex factors, changes in LBW incidence occur slowly. Estimates every five years are probably reasonable and consistent with the schedules of many large surveys (e.g., the DHS). Evaluators must recognize that this indicator will be slow to change, even with well-executed interventions.
nutrition, newborn (NB), malaria
Malaria in Pregnancy: Guidelines for measuring key monitoring and evaluation indicators. WHO, 2007.