Birth weight specific mortality rate (BWSMR)

The Birth Weight Specific Mortality Rate (BWSMR) is a stratification of a newborn mortality rate by birth weight grouping. (See indicator Neonatal mortality rate (NMR.)) For example, the Birth Weight Specific Neonatal Mortality Rate for births over 2,500g is calculated as:

(Number of neonatal deaths weighing over 2,500 g at birth / Total number of live births weighing over 2,500 g at birth) x 100

And for births under 2,500g is calculated as:

(Number of neonatal deaths weighing under 2,500g at birth / Total number of live births weighing under 2,500g at birth) x 100

Evaluators can calculate BWSMR for perinatal deaths and stillbirths on the same basis.


Number of deaths in a particular birth weight grouping and total number of births in the same weight grouping


Service statistics

HIS may collect data for this indicator in highly developed systems.


As discussed in the preceding sections, birth weight is one of the most sensitive predictors of infant survival and is also a good predictor of maternal health and well-being. The mortality rate for low birth weight babies is much higher than for those with a normal birth weight. Stratifying newborn deaths by birth weight helps to determine the cause of death and therefore to identify where interventions are needed. For example, deaths of very small babies are more likely related to maternal causes predisposing to intrauterine growth retardation and preterm birth, whereas deaths of normal birth weight babies are more likely to be related to intrapartum asphyxia and poor obstetric care. In the first case, interventions should focus on the mother (improving nutrition and reducing antenatal infection) and, in the second case, should focus on improving the quality of delivery care. Evaluators can obtain additional information by stratifying birth weight by time of death.

Potential Causes of Death for Specific Age and Birth Weight Categories

WeightFetal DeathIntrapartum Death

Early Neonatal Death

Late Neonatal Death
Less than 2500g

Maternal infection (e.g. malaria, syphilis, other STIs)

Medical complications

Antepartum hemorrage

Hypertensive disease

Complications of preterm labor/IUGR

Asphyxia

Complications of preterm labor/IUGR

Infections

Infections (ARI)

Late complications of prematurity

Tetanus

2500g and above 

Maternal infection (e.g. malaria, syphilis, other STIs)

Medical complications

Antepartum hemorrage

Hypertensive disease

Asphyxia and birth trauma

Maternal infection

Asphyxia and birth trauma

Infection

Infections (ARI)

Tetanus


Evaluators can collect this type of indicator only in settings where all babies are weighed. It is therefore most appropriate for use in health facilities but has served in some community settings as part of a maternal and perinatal health care surveillance system (McCarthy, Lawn, and Ross, 2001).

One useful application of this type of disaggregation is to examine the number of intrapartum deaths in normal birth weight babies. If the quality of obstetric care is good (and women are not presenting very late in labor), then very few intrapartum deaths should occur because deliveries are expedited rapidly. The proportion of stillbirths in babies of normal birth weight may serve as a proxy indicator for intrapartum asphyxia and quality of delivery care.

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