Morbidity in Late Preterm Birth: A Retrospective Cohort Study Assessing the Role of Immaturity versus Antecedent Factors

Abstract

Introduction: Late preterm infants (LPIs) are infants born between 340/7 and 366/7 weeks gestation. Morbidities in these infants are commonly considered a result of prematurity; however, some research has suggested immaturity may not be the sole cause of morbidities. We hypothesize that antecedents leading to late preterm birth are associated with different patterns of morbidities and that morbidities are the result of gestational age superimposed by the underlying etiologies of preterm delivery. Methods: This is a retrospective cohort study of late preterm neonates born at a single tertiary care center. We examined neonatal morbidities including apnea of prematurity, hyperbilirubinemia, hypoglycemia, and the requirement for continuous positive airway pressure (CPAP). Multivariable logistic regression analysis was performed to estimate the risk of each morbidity associated with 3 categorized antecedents of delivery, that is, spontaneous preterm labor, preterm premature rupture of membranes (PPROM), and medically indicated birth. We calculated the predictive probability of each antecedent resulting in individual morbidity across gestational ages. Results: 279 LPIs were included in the study. Decreasing gestational age was associated with significantly increased risk of apnea of prematurity, hyperbilirubinemia, and requirement of CPAP. In our cohort, the risk of hypoglycemia increased with gestational age, with the greatest incidence at 360-6 weeks. There was no significant association of risk of selected morbidities and the antecedents of late preterm delivery, with or without adjustment for gestational age, multiple gestation, small for gestational age (SGA), antenatal steroids, and delivery method. Discussion and Conclusion: This study found no difference in morbidity risk related to 3 common antecedents of preterm birth in LPIs. Our research suggests that immaturity is the primary factor in determining adverse outcomes, intensified by factors resulting in prematurity.