More than the passage of time: neonatal health and active labor duration, the mediating role of chorioamnionitis

Labor intervention is intended to prevent perinatal morbidity and mortality. Labor durations traditionally defined as “dystocia” affect primary cesarean delivery rates. However, there is mixed evidence about the association between labor duration and poor neonatal outcomes. Using latent class analysis to study unknown patterns of neonatal health can refine the understanding of these relationships and the effects of labor duration on newborn outcomes. This study aimed to (1) identify latent classes of newborn health characteristics; (2) describe pregnancy and labor characteristics of individuals in the classes, including active labor duration; (3) determine the probability of class membership (newborn health) using labor duration and associated factors as predictors; and (4) assess direct and indirect effects of labor duration vs chorioamnionitis on neonatal risk. This was a latent class analysis of 3779 term, cephalic, singleton, and nonanomalous maternal/child dyads using prospectively collected observational data. Latent class analysis of 3779 term, cephalic, singleton, and nonanomalous maternal/child dyads identified 6 neonatal phenotype classes: 4 (classes 1–4; 92% of the data) with normal neonatal outcomes and 2 (classes 5 and 6) with abnormal neonatal outcomes. Apgar scores were not related to more severe markers of neonatal well-being (neonatal intensive care unit admission, morbidity diagnosis, and failure to discharge home when the parent was discharged). Although the median labor duration was longer in classes 5 and 6, most women had labors in the lower 3 quartiles. Most births in the longest quartile of labor were associated with healthy newborn outcomes. Chorioamnionitis mediated 26% of the relationship between labor duration and newborn health phenotype. Neonatal risk may be driven or mediated by several labor and birth factors, many of which are challenging to disaggregate. Previous research presuming longer labor duration as the driver of neonatal risk may have masked other relevant associations. More research on physiological vs pathologic inflammatory and infectious processes during term labor is crucial for advancing labor dystocia research and refining intrapartum management. Additional variables strongly correlated with labor dystocia (eg, fetal malposition) should be examined as potential mediators between longer labor and poor neonatal outcomes. [Display omitted]