Chapter 41

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 mortality rate.

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 of ...

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