What is Impact of Latent Labor Phase Duration on Birth Outcomes?

In previous research on labor duration and outcomes, there has been less emphasis on the latent phase of the first stage of labor. Past literature used different definitions for the start and end of the latent phase of labor. A systematic review found that the majority of studies (79%) included cervical dilation as part of their definition for the onset of the latent phase of labor. Recent study aimed to characterize the duration of the spontaneous onset of the latent phase of labor using contemporary definitions of latent labor onset and termination, and examine the association between the duration of the latent phase of labor and perinatal processes and outcomes during the active first and second stages of labor, delivery, and immediately after delivery. T

he key findings were: 1. The duration of the latent phase of labor in nulliparous women, beginning with the perception of the onset of painful contractions and terminating at 5 cm cervical dilation, was longer than previous characterizations. The median duration was 16 hours for nulliparous women and 9.4 hours for multiparous women. 2. Longer duration of the latent phase of labor increased the risk of a diagnosis of labor dystocia and related interventions, including cesarean delivery, in the first stage active phase or second stage of labor. 3. A latent phase duration >90th percentile was associated with a higher relative risk, but low absolute risk, of poor neonatal outcomes like low Apgar scores and NICU admission, especially in nulliparous women. It was also associated with higher rates of chorioamnionitis and fetal occiput posterior position.

Implications and Conclusion

The results highlight the need for more research on how progress of the latent phase may shape the overall labor trajectory, and what factors may mediate the association between prolonged latent phase and increased neonatal risk. The longer latent phase durations found using contemporary definitions suggest this phase warrants closer attention in both clinical practice and research on labor management and outcomes.

Key Points

1. The duration of the latent phase of labor in nulliparous women, beginning with the perception of the onset of painful contractions and terminating at 5 cm cervical dilation, was longer than previous characterizations. The median duration was 16 hours for nulliparous women and 9.4 hours for multiparous women

2. Longer duration of the latent phase of labor increased the risk of a diagnosis of labor dystocia and related interventions, including cesarean delivery, in the first stage active phase or second stage of labor.

3. A latent phase duration >90th percentile was associated with a higher relative risk, but low absolute risk, of poor neonatal outcomes like low Apgar scores and NICU admission, especially in nulliparous women. It was also associated with higher rates of chorioamnionitis and fetal occiput posterior position.

4. The results highlight the need for more research on how progress of the latent phase may shape the overall labor trajectory, and what factors may mediate the association between prolonged latent phase and increased neonatal risk.

5. The longer latent phase durations found using contemporary definitions suggest this phase warrants closer attention in both clinical practice and research on labor management and outcomes.

6. The study aimed to characterize the duration of the spontaneous onset of the latent phase of labor using contemporary definitions of latent labor onset and termination, and examine the association between the duration of the latent phase of labor and perinatal processes and outcomes during the active first and second stages of labor, delivery, and immediately after delivery.

Reference -

Tilden EL, Caughey AB, Ahlberg M, Lundborg L, Wikström AK, Liu X, Ng K, Lapidus J, Sandström A. Latent phase duration and associated outcomes: a contemporary, population-based observational study. Am J Obstet Gynecol. 2023 May;228(5S):S1025-S1036.e9. doi: 10.1016/j.ajog.2022.10.003. Epub 2023 Mar 15. PMID: 37164487; PMCID: PMC10172685.