Prevalence of Prolonged Latent Phase and Labor Outcomes: Review of Birth Records in a Swedish Population.

INTRODUCTION: The prevalence of a prolonged latent phase of labor has been described as ranging from 5% to 6.5% in previous research. The aim of this study was to describe the prevalence of the prolonged latent phase of 18 hours or more, based on women's report, in women intending vaginal birth and who had spontaneous onset of labor. An additional aim was to compare the incidence of obstetric interventions, and the labor and neonatal outcomes in women with and without a prolonged latent phase.
METHODS: A descriptive and comparative study was performed in a mid-sized hospital in western Sweden. The sample consisted of 1343 birth records of women who intended vaginal births and who had spontaneous onset of labor at 37 or more weeks' gestation during a one-year period (2013-2014). Background characteristics, obstetric interventions, and labor and neonatal outcomes were compared between women with latent phases lasting less than 18 hours and 18 hours or more, based on women's self-report. Odds ratios with 95% confidence intervals were calculated for the different exposure variables.
RESULTS: A prolonged latent phase lasting 18 hours or more occurred in 23% of all births analyzed (n = 1343). A prolonged latent phase was more common among nulliparous women (29.2%) but also common for multiparous women (17%). Nulliparous and multiparous women who experienced a prolonged latent phase were more often exposed to amniotomy during latent phase. For nulliparous women, the adjusted odds ratio (aOR) was 11.57 (95% confidence interval [CI], 5.25-25.51) and for multiparous women the aOR was 18.73 (95% CI, 9.06-38.69). Similarly, amniotomy during active phase was more common for both nulliparous and multiparous women who experienced a prolonged latent phase (aOR, 4.05; 95% CI, 2.53-6.47 and aOR, 3.93; 95% CI, 2.43-6.37, respectively). Women with latent phases of 18 hours or more, more often experienced augmentation of labor during all phases, especially during latent phase. For nulliparous women, the aOR was 10.13 (95% CI, 2.82-36.39) and for multiparous women, aOR was11.9 (95% CI, 3.69-38.71). A prolonged latent phase was associated with more instrumental vaginal births for multiparas (aOR, 2.58; 95% CI, 1.27-5.26) and emergency cesarean regardless of parity (nulliparous women: aOR, 3.21; 95% CI, 1.08-9.50 and multiparous women: aOR, 3.93; 95% CI, 1.67-9.26). DISCUSSION: Based on women's self-report, the prevalence of a prolonged latent phase in women at term who planned a vaginal birth and had spontaneous onset of labor was higher than previously reported. Women with a prolonged latent phase were more likely to receive obstetric interventions. Assisted vaginal birth was more common for nulliparous women with prolonged latent phase and emergency cesarean occurred more frequently for both nulliparous women and multiparous women with a prolonged latent phase.