Safe labor : reappraisal of labor duration and management for safe maternal and infant outcome

Sammanfattning: Background: The partograph, today used worldwide for assessing normal labor progress and identifying prolonged labor is based on Friedman’s research findings from the 1950s, based on 500 deliveries. Friedman established a series of definitions of time parameters, labor curves and phases to detect normal and abnormal labor progress and incorporated it into the Partograph. However, since the early 2000s, there is increasing evidence suggesting that the described relationship between cervical dilatation and duration of the first stage of labor may be inappropriate, which could be due to a misinterpretation of Friedman’s and others’ findings. Importantly, contemporary changes in maternal demographics and obstetrical management raise serious concerns to whether Friedman ́s definitions can be applied to contemporary childbearing women. Improved understanding of correct thresholds for what should be defined as normal labor progression and duration is important to improve every aspect of childbirth. Therefore, the overall aim of this thesis was to establish updated and evidence-based measures of normal labor duration, focusing on labors with spontaneous onset. Methods: All four studies were population-based cohort studies with data from the Stockholm Gotland Obstetric cohort. The study population was term gestations with spontaneous labor onset. In Study I we investigated duration of the first stage of labor and trajectory of cervical change in both nulliparous and multiparous women. Study II investigated the association between body mass index (BMI) and first stage labor duration, the outcome was first stage labor duration and the analysis were stratified by BMI class and tested for effect modification of age. The study population was term gestations with spontaneous labor onset, allocated to Robson group 1. Study III investigated our hypothesis that labor duration is a continuous process. The study population was term gestations with spontaneous labor onset, allocated to Robson group 1. The relationship between the active first stage of labor and second stage duration was examined at different quantiles and the linear association was modelled using restricted cubic splines. Multinomial logistic regression was used to test the association between increasing active first stage duration and mode of delivery. In Study IV the relationship between increasing active first stage of labor duration and adverse neonatal outcomes was examined. The study population was term gestations with spontaneous labor onset, allocated to Robson group 1. Here, the investigated outcome was a composite of either moderate or severe outcomes. Modified Poisson regression was used to test the association at different thresholds of labor duration and relative risks with 95% confidence intervals (CI) were calculated. Main findings: Labor progression and duration varied largely between women, indicating that using measures of central tendency is not useful to identify slow labor. Labor does not seem to accelerate until beyond a cervical dilation of 5-6 cm. Obese women had longer active first stage and total active labor duration and this association was modified by age. Increasing duration of active first stage of labor was also associated with a linear increase of duration of second stage of labor until a plateau at 12 hours of first stage duration. Risk for adverse neonatal outcomes was increasing along with a cumulatively increasing duration ranging from 5-10 hours, we tested the association in relation to two composite neonatal outcomes, based on clinical knowledge of severity and risks of long-term consequences. The risk for moderate neonatal outcome started to increase from 5.1 hours (aRR 1.40, CI 1.24, 1.58) and were twofold increased for women beyond the 90th percentile (10.1 hours). Moreover, among severe neonatal outcomes the risk was found significant beyond the 90th percentile (10.1 hours, aRR 1.53, CI 1.26, 1.87). Effect decomposition showed that only approximately 1/5 of the found association was mediated by second stage of labor duration for moderate neonatal outcomes. For severe outcomes with a labor duration beyond the 90th percentile (10.1 hours), approximately 13 % of the association was mediated through second stage of labor duration. Conclusions: Variations in both the total duration and the trajectory of cervical change over time was large and the progressive pace of cervical dilation is found around cervical dilation of 5–6 centimeters. Labor duration is a continuous process, BMI and Age and labor duration during the active first stage will have impact on labor duration and interventions in second stage. The biological interpretation is that labor duration and progression is a function of observed and unobserved maternal and neonatal anthropometrics and management norms, which cannot be constrained into a model where one duration or one pace fits all. Adverse neonatal outcomes are rare, and any implications of a duration threshold for when the absolute risk of an event occurs is not possible to establish, however the relative risk increased with increasing duration at different examined percentiles, i.e. 5, 7 and 10 hours of labor duration. Implications: The findings from all studies within this thesis may safeguard against potential unintended fatal consequences of practice change based on average separate thresholds for slow progression during first and second stage of labor. Vice versa, potential unintended consequences of a “better safe than sorry regime” needs to be balanced against the risk of long-term consequences for both mother and neonate with terminating labor during due to slow labor per se. Future research should aim to identify those women and fetuses who are vulnerable to longer labor durations to provide clinicians and pregnant women with information about who can continue with labor and who ́s labor that should be terminated earlier. Consequently, it would also be beneficial with more research emphasis on the etiologic causes for slow labor to customize any use of interventions during childbirth.

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