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I. INTRODUCTION

The most commonly agreed upon definition of a late preterm infant is an infant born between 34 0/7 and 36 6/7 weeks’ gestation. Older literature refers to these infants as near term, suggesting that they are equivalent to term infants. Approximately 10 years ago, the term late preterm was introduced into the medical literature to convey an appropriate sense of these infants’ vulnerability and increased risk for both short- and long-term complications. Since 2007, >500 articles about late preterm infants have been published, underscoring the increased risk of morbidity and mortality compared to term infants.

Late preterm births represent approximately 74% of all preterm births. Between 1992 and 2007, the incidence of late preterm births increased from 7.3% to 10.4% of all births. More recently, the rate of late preterm births has decreased to 9.6% in 2014, representing an 8% drop from 2007. This is likely related to an improved understanding of the increased risk of poor neonatal outcomes in this population.

II. POTENTIAL ETIOLOGIES

Improvements in obstetrical surveillance over time may contribute to an increased incidence of medically indicated premature deliveries. Recent recommendations from the American College of Obstetricians and Gynecologists that discourage induction or scheduled repeat cesarean deliveries before 39 weeks, as well as specific guidelines for criteria for elective preterm delivery, likely contributed to the decreased rate of late preterm births seen over the past several years. However, not all late preterm deliveries are preventable, and potential etiologies include the following:

  1. Preeclampsia

  2. Spontaneous preterm labor and preterm premature rupture of membranes

  3. Multifetal gestations

  4. Antepartum bleeding

  5. Fetal growth restriction

III. COMPLICATIONS OF LATE PRETERM BIRTH

  1. Mortality. A systematic review investigating the outcomes of >2 million late preterm infants found that these infants were 5.9 times more likely to die within the first 28 days of life as compared to term infants. While the absolute number of deaths of late preterm infants is low, the relative risk is high.

  2. Respiratory morbidity. A large systematic review showed that late preterm infants are 17.3 times more likely to develop respiratory distress syndrome than term neonates. This is secondary to immature lung architecture, surfactant deficiency, and deprivation of normal hormonal changes occurring at term that promote the clearance of lung fluid. The risk of respiratory distress increases with decreasing gestational age (relative risk [RR] of 10.9 in 36-week infants, 28.6 in 35-week infants, and 48.4 in 34-week infants). Late preterm infants are also 4.9 times more likely to require intubation and mechanical ventilation, 9.8 times more likely to need CPAP, and 24.4 times more likely to require nasal oxygen compared to term infants. In one review, 11% of late preterm infants with respiratory failure developed chronic lung disease and 5% died, emphasizing the serious long-term consequences of respiratory complications in this population.

  3. Length of stay. Studies show that late preterm infants have ...

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