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  1. Introduction. The increased number of infants who deliver between 34 and 37 weeks is a vexing problem for pediatric and obstetric practitioners alike. It has been the subject of growing interest and concern that has generated new research into the causation as well as the appropriate management of these patients.

    The most agreed-on definition of late preterm infants are those born between 34 0/7 and 36 6/7 weeks' gestation. Older literature refers to these infants as "near term," suggesting they are equivalent to term infants. Recently, the consensus is to refer to these infants as "late preterm," which conveys an appropriate sense of their vulnerability.

    Between 1992 and 2002, late preterms increased from 7.3–8.5% of all births, a 16% increase. They now represent about three quarters of all preterm births. Davidoff demonstrated the median gestational age at delivery for singletons born in the United States is now 39 weeks. Another study showed that infants born at 34 weeks were 4.6 times more likely to die than those at 40 weeks, which contributes significantly to the neonatal mortality rate.

  2. Potential etiologies. Although the exact causation of increased late preterm delivery remains elusive, the rate must be rising due to increased medical interventions at or beyond 34 weeks.

      1. Preeclampsia is the most common complication of pregnancy occurring in between 6% and 10% of pregnancies and is rising. Studies are conflicting as to whether the increase in late preterm deliveries is due to preeclampsia.

      1. Preterm labor and premature rupture of membranes may lead to late preterm delivery but are not currently preventable.

      1. Multifetal gestations are rising due to advanced parental age from delayed childbearing and artificial reproductive technology (ART). Multiples contribute to late preterm delivery by virtue of earlier gestation at delivery, unique obstetric complications, and an increased risk of intrauterine growth restriction and preeclampsia. Interventions to prevent preterm delivery in multiples have been ineffective. Refinement in ART leading to decreased numbers of multifetal gestation may help decrease their contribution to late preterm deliveries.

      1. Stillbirths have declined from 14 to 6.7 per 1000 live births since 1970. There were 27,000 stillborns in 1998 equivalent to the annual deaths from prematurity and sudden infant death syndrome (SIDS) combined. Current research does not support stillbirth prevention as a cause of late preterm delivery.

  3. Complications of late preterm birth

      1. Respiratory distress syndrome (RDS). In one large study, 21% of infants born at 33 weeks, 7.3% at 35–36 weeks, and 0.6% at 37–42 weeks had RDS. Late preterm infants are deprived of the normal hormonal changes that occur at term and promote the clearance of lung fluid. In the United States, 17,000 infants >34 weeks are admitted to neonatal intensive care units (NICUs) annually, accounting for up to a third of NICU admissions. In another review, 11% of late preterm infants with respiratory failure developed chronic lung disease and 5% died.

      1. Length of stay. Wang et al found that late preterm infants had a similar median length of stay as term infants but with ...

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