Infant mortality is an important outcome measure of the health
services of a population. In the United States, where there are
approximately 4 million births each year, the infant mortality is
around 7 per 1000 live births. The highest risk of infant death
is within 24 hours of birth, but mortality and morbidity remain
high during the neonatal period, from birth to the 28th day of life.
In the United States each year, nearly 1% of pregnancies
are complicated by fetal death and about 0.5% by neonatal mortality.1-8The
fetus and newborn are most vulnerable during labor, delivery, and
the neonatal period because central nervous system injury may result
in lifelong morbidity and neurodevelopmental impairment. The perinatal
period, from 28 weeks of gestation to the 28th day of life, is the period
of greatest mortality. In the modern era, with survival of extremely-low-birth-weight infants,
postneonatal mortality also contributes significantly to the infant
The reduction of maternal and infant mortality and the improvement
of the health of mothers and infants in the United States are high
priorities. Statistical comparisons among countries, states, regions,
and individual centers have been hampered by differences in definitions. In
order to compare outcomes and plan interventions, it is imperative
that standard definitions be utilized9:
- Appropriate for gestational age (AGA): An infant
with a birth weight between the 10th and 90th percentiles for that
gestational age. Those below the 10th percentile are regarded as
small for gestational age (SGA), whereas those above the 90th percentile
are considered large for gestational age (LGA).
- Birth weight: The weight of a neonate determined
immediately after delivery or as soon thereafter as feasible, expressed
to the nearest gram.
- Fetal death: Death before the complete expulsion
or extraction from the mother of a product of human conception,
fetus and placenta, irrespective of the duration of pregnancy; the death
is indicated by the fact that after such expulsion or extraction,
the fetus does not breathe or show any other evidence of life, such
as beating of the heart, pulsation of the umbilical cord, or definite
movement of voluntary muscles. Heartbeats are to be distinguished
from transient cardiac contractions; respirations are to be distinguished
from fleeting respiratory efforts or gasps. This definition excludes
induced termination of pregnancy.
- Gestational age: The number of weeks that have
elapsed between the first day of the last normal menstrual period
(not the presumed time of conception) and the date of delivery, irrespective
of whether the gestation results in a live birth or a fetal death.
- Infant death: Any death at any time from birth
up to, but not including, 1 year of age.
- Live birth: The complete expulsion or extraction
from the mother of a product of human conception, irrespective of
the duration of pregnancy, which, after such expulsion or extraction,
breathes or shows any other evidence of life, such as beating of
the heart, pulsation of the umbilical cord, or definite movement
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