The past 20 years witnessed an invigoration of research on labor progression and a change of thinking regarding normal labor. New evidence is emerging, and more advanced statistical methods are applied to labor progression analyses. Given the wide variations in the onset of active labor and the pattern of labor progression, there is an emerging consensus that the definition of abnormal labor may not be related to an idealized or average labor curve. Alternative approaches to guide labor management have been proposed; for example, using an upper limit of a distribution of labor duration to define abnormally slow labor. Nonetheless, the methods of labor assessment are still primitive and subject to error; more objective measures and more advanced instruments are needed to identify the onset of active labor, monitor labor progression, and define when labor duration is associated with maternal/child risk. Cervical dilation alone may be insufficient to define active labor, and incorporating more physical and biochemical measures may improve accuracy of diagnosing active labor onset and progression. Because the association between duration of labor and perinatal outcomes is rather complex and influenced by various underlying and iatrogenic conditions, future research must carefully explore how to integrate statistical cut-points with clinical outcomes to reach a practical definition of labor abnormalities. Finally, research regarding the complex labor process may benefit from new approaches, such as machine learning technologies and artificial intelligence to improve the predictability of successful vaginal delivery with normal perinatal outcomes.

BACKGROUND: The purpose of this study is to conduct an overview of Cochrane systematic reviews (SRs) evaluating the effects of maternal positions in childbirth in order to compile existing evidence for relevant research questions that have been addressed by more than one review, to provide a succinct summary of the up-to-date evidence and to identify areas for future research.
METHODS: An electronic search was conducted in the Cochrane database. Two primary outcomes were the duration of labor and birth, and operative birth. The quality of included reviews was assessed using the AMSTAR criteria, and the quality of the evidence was rated using the GRADE criteria.
RESULTS: We included 3 Cochrane SRs. There was a significant mean difference (MD) found in the duration of the first stage by 1 hour and 22 minutes (MD= -1.21; 95% CI: -2.35 - -0.07, I2=94%) and reduction in caesarean section rates (RR=0.71; 95% CI: 0.54-0.94, I2=0%) in the upright birth position group compared with the horizontal. Also, there was a statistically significant difference in the duration (minutes) of the second stage of labor (MD= -6.16; 95% CI: -9.74 - -2.59, I2=91%) and a reduction in assisted vaginal birth rates (RR=0.75, 95% CI: 0.66-0.86, I2=29%) in the upright group compared with the horizontal without epidural analgesia. The quality of evidence within the reviews was very low to moderate.
CONCLUSIONS: There is currently a limited body of evidence to clearly assess the benefits and risks of assuming upright positions during childbirth. The overview highlights the need for high-quality research studies, involving better definition and comprehensive assessment of the effects of squatting during childbirth.