Neonatal Deaths

A neonatal death is death of an infant prior to the 28th day of life. Demographers and epidemiologists define the neonatal mortality rate (NMR) as:

where

Deathsz<28days refers to deaths to infants younger than 28 days old, in year z; and

Birthsz is the number of live births in year z.

Neonatal deaths are usually examined separately from other infant deaths occurring during the first year of life. This distinction is made because (a) there is very high mortality during the first minutes, hours, days, and weeks of life, and (b) the causes of death in the neonatal period tend to differ from the causes in the postneonatal period (28 days to 364 days after birth).

Primary Causes of Neonatal Mortality

In 2005, about 30#x0025; of all neonatal deaths occurring in the United States were due to prematurity, or being born before 37 weeks of gestation. Generally, the more premature the infant, the more likely death will occur. Only about 20#x0025; to 35#x0025; of babies born at 23 weeks of pregnancy survive, compared to 50#x0025; to 70#x0025; of those born at 24 to 25 weeks. Survival increases to more than 90#x0025; at 26 to 27 weeks' gestation, whereas births before 32 weeks' gestation, comprising about 2#x0025; of all births, account for most neonatal deaths and disorders.

Premature births occur after spontaneous premature labor (50#x0025; of cases), a spontaneous rupture of the membranes (30#x0025; of cases), and intentional [Page 782]delivery of a premature infant for the benefit of the infant and/or mother (20#x0025; of cases). Causes of preterm birth that are the consequences of the mother's health include high blood pressure, placental problems, a previous preterm delivery, a multiple birth, and abnormalities in the uterus or cervix.

Neonatal deaths also result from structural and genetic birth defects such as spina bifida, anencephaly, and heart or kidney defects. Birth defects account for around 21#x0025; of all deaths to infants in the United States recorded during 2005. Defects where the heart and lungs do not develop fully are the most common cause of neonatal death. Abnormalities in which the infant has more or less than the normal 46 chromosomes represent a common cause of neonatal death. It is rare for embryos with chromosomal abnormalities to survive the pregnancy, but those who do will likely die within the first few weeks of life. Other less prominent causes that account for the almost 40#x0025; of remaining neonatal deaths include pregnancy related problems, such as complications involving the placenta or problems with the umbilical cord and membranes.

Variation in Neonatal Mortality

Every year four million infant deaths occur during the neonatal period. Globally, 99#x0025; of neonatal deaths are in lowor middle-income countries. The largest numbers of neonatal deaths occur in southcentral Asian countries with the highest rates in sub-Saharan Africa. Worldwide, the main cause of neonatal deaths is preterm birth (28#x0025;), severe infections (26#x0025;), and asphyxia (23#x0025;).

In developed countries, around two-thirds of all infant deaths occur during the neonatal period and are often due to preterm delivery or birth defects. There has been a dramatic decline in the NMR due to low birth weight mortality, whereby almost 80#x0025; of the deaths are to birth weights of less than 750 grams. This decline is believed to be due to technical strides in obstetrics, neonatal intensive care, and policies that provide health care access to disadvantaged groups.

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