Late-Preterm Births: Challenges and Opportunities

Until the 1980s, the phrase “near term” was used only as an adjective to identify research subjects (or study animals) close to term gestation.1–3 For unknown reasons, the phrase gradually assumed a wider, physiologic connotation. An ill-defined group of infants began to be labeled near term, which implied that they were “almost term” and, hence, there was no reason for concern. Two factors might have contributed to such shifts in perception. In obstetric practice, 34 completed weeks of gestation began to be considered a maturational milestone, beyond which active interventions are rarely undertaken to prevent preterm births.4 In randomized, controlled trials (which became increasingly popular since the 1980s) and in outcomes studies, women at term and near-term gestations, or their infants, were being combined into single entities, a practice that has continued.5–8 Thus, our collective perception on term and near-term infants might have slowly changed so that these infants are seen as a homogeneous group with regard to morbidity and mortality profiles.Whatever the reason for such assumptions, accumulating research is proving that prematurity by even a single week increases the risk for neonatal morbidity and mortality.9–11 An expert panel has suggested that the phrase “near term” be replaced with “late preterm” to convey the sense that infants who are born between 34 through 36 weeks of gestation are immature and vulnerable and need close monitoring, evaluation, and follow-up.11 Compared with term infants, late-preterm infants are at higher risk for readmissions, postneonatal mortality, sudden infant death syndrome, white matter injury, and neurodevelopmental problems well into school age.12–15A report in this month's Pediatrics Electronic Pages by Shapiro-Mendoza et al16 adds another dimension to the growing number of research studies that reinforce the vulnerability of late-preterm infants. Using a unique, statewide data set, the investigators found that late-preterm infants were at sevenfold higher risks for neonatal morbidity compared with term infants. More dramatically, the rates of morbidity doubled for each gestational week earlier than 38 weeks, such that even at 37 weeks (the first week of the term gestation) the morbidity rates were twice those at 38 weeks. Instead of using birth-certificate data, the investigators verified hospital discharge summaries and found a strong association between maternal illness and neonatal morbidity. Compared with term infants, existence of maternal illness further increased morbidity risks for those in the late-preterm group. This is the first report to provide such an important association.Taken together, the above-mentioned study and such similar research reports on late-preterm births have major implications for obstetric and neonatal care. Maturation is a continuum, and any preset gestational age cannot be assumed to provide a clear separation between immaturity and maturity. Because all preterm infants carry finite, measurable risks, the indications for preterm deliveries need to be justified. In the presence of maternal or fetal illnesses, the risks and benefits of immediate delivery versus postponing it need to be closely assessed. Because the preterm birth rate is increasing,17 and the late-preterm group (which constitutes >70% of all preterm births) is the fastest growing subset,18 even a small increase in their morbidity rate can have a major impact on the health care burden.Despite much research, the reasons for the increasing number of preterm births are unclear, especially because there have been no reports of increasing prevalence of traditional risk factors such as preeclampsia, umbilical cord accidents, and chorioamnionitis. Advancing maternal age, an often-cited factor for the increasing preterm birth rate, cannot explain all such increases. Increasing rates of multifetal gestation also cannot explain the increasing rate of late-preterm births among singleton pregnancies.Some investigators have suggested that nontraditional factors may need to be explored to explain increasing late-preterm birth rates.19 Questions that need to be addressed include: Do some health care providers use “soft” indications for induction of labor in late-preterm pregnancies? Have the improved standards of neonatal care led to a sense of complacency concerning late-preterm births? Do some patients request early labor inductions (and their obstetricians oblige) for the sake of mutual conveniences? If so, how common are such practices? Are there variations in standards of care for late-preterm pregnancies across regions or between academic versus nonacademic centers, rural versus urban communities, and private versus public payer systems?One hopes that future research will yield answers to these critical questions. In the meantime, obstetricians need to avoid delivery of infants in late-preterm pregnancy when it is not medically indicated. Those who care for late-preterm infants need to recognize that such infants are physiologically immature even when they appear clinically “stable.” All late-preterm infants need to be diligently evaluated, monitored, and followed up.