Does Birth at Early-Term Gestation Increase Mortality for Neonates on Extracorporeal Life Support After Cardiac Surgery?*

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Babies born in the early term period, defined by the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine as 37 to less than 39 weeks of gestation (1), have been recognized to fare worse than those born at full term (39–40 weeks of gestation). Early-term neonates have a higher frequency of sepsis, hypoglycemia, greater requirement for respiratory support after birth, higher rates of admission to neonatal intensive care, and prolonged in-patient stay (2–4). Organ immaturity has been postulated as the potential reason for poor outcome.
These findings are especially true in babies with congenital heart disease (CHD) born at early-term gestation. Several recent studies have demonstrated this (5–7). Costello et al (6) examined this association with an analysis of more than 4,000 neonates from 92 hospitals in the Society of Thoracic Surgeons Congenital Heart Surgery Database who underwent surgery between 2010 and 2011. Delivery at 39–40 weeks of gestation was consistently associated with the lowest rates of early morbidity and mortality. Maturational differences in multiple organ systems were considered most likely contributory to the adverse outcomes experienced by neonates with CHD born at early term. In-hospital morbidity and mortality differences are further compounded by worse neurodevelopmental outcomes after cardiac surgery in neonates born early term (8). This is of particular relevance to outcomes for neonates with CHD as many tertiary centers plan delivery of fetuses prenatally diagnosed with CHD around early-term gestation to better coordinate their complex postnatal management (5). The American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine have recommended avoiding early-term delivery when not medically indicated (9).
Mechanical circulatory support (MCS) is used in the perioperative period for between 9% and 17% of neonates with CHD undergoing the most complex cardiac surgical procedures (10). Reports of extracorporeal membrane oxygenation (ECMO) use in this population from the Extracorporeal Life Support Organization Registry have shown that both lower gestational age and birthweight are associated with increased in-hospital mortality (11, 12). Poor survival in lower gestational age neonates may be explained by the higher incidence of neurologic injury resulting from brain immaturity (13). An association with early-term gestation and ECMO survival in neonates with CHD has not been previously reported.
In this issue of Pediatric Critical Care Medicine, McKenzie et al (14) investigate survival following postoperative MCS in full term compared with early-term gestation neonates with CHD. In this single-center study, they included 110 neonates supported with MCS after cardiac surgery over a 10-year period. Patients in the study were supported with ECMO or ventricular assist devices. Their main finding was that full term compared with premature (31–36 weeks of gestation) neonates with CHD supported by MCS after cardiac surgery had lower odds of ICU mortality. Mortality for early-term (37–38 weeks of gestation) neonates was similar to preterm infants. Thus, the authors infer that mortality was higher in early term compared with full-term gestation neonates. Like previous studies cited here, the authors postulate that improved survival in full-term neonates resulted from improved organ maturation.
Making a meaningful assessment of the impact of ECMO on cardiac surgical survival in the CHD population is challenging, as many factors including severity of CHD diagnosis, timing of ECMO deployment, and ECMO management strongly influence survival (11, 15). Given that neonates with CHD born at early term compared with full-term gestation have increased morbidity, mortality, and resource use, the independent contribution of MCS to mortality in this context is unclear. Thus, McKenzie et al (14) do not provide compelling evidence to support the association between MCS and reduced survival in postsurgical early-term neonates with CHD.

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