The studies in our review focused on the active phase of labour rather than the latent phase, which is relevant given the adverse outcomes associated with early hospitalisation in the latent phase [2, 3, 30]. A strong consensus on the definition of the onset of latent contractions is needed to ensure comparability of research findings and subsequently guide clinical diagnosis and intervention. Understanding when the transition between latent and active phases of labour occurs is essential for developing initiatives that help women stay out of hospital during the latent phase of labour . Of the 11 studies that defined the onset of the first phase of labour without reference to a specific phase [32-34, 38, 47, 62, 68-70, 73, 78], five (45%) provided specific cervical dilation in their definition, including four that defined the onset of labour in the first stage, when the cervix was 3-4 cm dilated [34, 38, 68, 69] and one study using a cervical dilation of ≥4 cm . Three studies did not quantify dilation, but found that there should be a “cervical change” in the first stage of labour onset [32, 33, 70]. Only one study defining labour in the first stage included extinction in its definition (9%) and only mentioned that there should be detectable extinction and dilation of the cervix in its definition of the first stage of labour . Gülmezoglu AM, Villar J, Ngoc NT, et al. WHO multicentre randomised study of misoprostol in the management of the third stage of labour. Lancet. 2001 September 1 358(9283):689-95.
[Medline]. Before beginning data extraction, the six full-text reviewers independently tested the standardized data extraction form on a random sample of three of the included studies . Responses were compared to account for discrepancies and all evaluators were involved in revising the data extraction form to ensure consistency and improve data quality. Once the form was completed, full-text reviewers (SM, GH, PJ, MG, HS and VH) independently extracted data from the studies. Each study was extracted by two reviewers, including one of the original reviewers (SM, GH and PJ). We did not contact study authors to confirm data. As our main interest was to define the onset of birth rather than the validity of the conclusion or study results, we did not assess risk of bias in our included studies. During the study inclusion period (1978-2013; see Fig. 2), no temporal pattern was observed with respect to the types of labour onset defined by the studies (i.e., latent vs. active) or the measures of cervical dilation (i.e., 3 cm versus 4 cm) that the studies used to define the onset of labour.
Instead, the studies used heterogeneous definitions over the entire period. However, the majority of studies that defined the onset of labour differently for nulliparous and multiparous women were published in 1986 or earlier [40, 41, 54, 66]. Gharoro EP, Enabudoso EJ. Work management: evaluation of the role of bad work and latent phase on the mode of delivery. J Obstet Gynaecol. 2006;26(6):534–7. Tabassum S, Afridi B, Aman Z. Phloroglucinol for acceleration of labour: a double-blind randomised controlled trial. J Pak Med Assoc. 2005;55(7):270–3. MM brut, Burian RA, Fromke C, Hecker H, Schippert C, Hillemanns P. Beginning of labour: women`s experiences and midwives` assessments of the duration of the first phase.
Arc gynecol obstet. 2009;280(6):899–905. In order to clarify the concepts around the definition of the beginning of latent and active phases of work and to determine the scientific justification on which these definitions are based, we conducted a systematic review of the literature. Our review asks: 1) How are the onset of the latent phase and the active phase of labour defined in healthy women who work spontaneously? and 2) What evidence, if any, does the authors provide to support their definitions of early birth? van Coeverden de Groot HA, Vader CG. The normal working hours among Cape whites. S Afr Med J. 1978;54(27):1125–9. Maghoma J, Buchmann EJ.
Maternal and foetal risks associated with prolonged latent labour phase. J Obstet Gynaecol. 2002;22(1):16–9. Despite research highlighting the importance of duration and transition between the latent and active phases of work, there are significant inconsistencies in definitions of early labour, a necessary component of measurement duration. The onset of the latent phase of labour has been defined as the time of the first clinical assessment of labour in hospital [3, 5], or alternatively the onset of regular painful strong contractions . Similarly, there are inconsistencies in the definitions of transition from latent to active. This important indicator of labour progression has been variously characterized to coincide with the onset of regular labour , beginning with when the woman was admitted to maternity , when she sought professional care  or when she consented to participate in a randomized controlled trial . More recently, researchers have used the woman`s self-report as a time of onset of labor [8, 12-14]. There is little consensus on definitions of early birth in the research literature.
To avoid misdiagnosis and identify deviations from normal work patterns, a consistent and measurable definition of the start of work is essential for each phase and stage. When selecting standard definitions, it is also necessary to consider the effects of their use on maternal and fetal morbidity rates. The thirteen studies (100%) that provided definitions for the onset of latent phase contractions included the presence of regular painful contractions in their definition [2, 28, 29, 40, 54, 55, 60, 67, 72, 75, 76, 81, 82]. Three studies (23%) reported that during the onset of the latent phase of labour, at least one painful uterine contraction should occur every 8–10 minutes [29, 54, 55], and one study stated that there should be at least two painful uterine contractions every 10 minutes . The duration of each contraction has not been taken into account in these definitions. Only three studies (23%) included other physiological symptoms in their definitions. These included a bloody spectacle [29, 72, 76] and fluid loss [72, 76], as well as gastrointestinal symptoms or irregular (unrepeated) pain [72, 76]. Bataille A, Rousset J, Marret E, et al. Ultrasound examination of gastric contents during labour under epidural analgesia: a prospective cohort study. F.
J Anaesth. 8 January 2014 [Medline]. More than half of the studies that defined the onset of active labour included regular painful contractions in their definition (n = 20.60%) [2, 28, 29, 35, 50, 51, 54, 56, 60, 61, 65-67, 71, 72, 74, 77, 81-83]. Of the studies that defined the onset of active labor, two showed that contractions should be spaced five minutes apart [66, 67], and two indicated that there should be at least three contractions in ten minutes [71, 74], while two more proposed contractions should occur every 3-5 minutes [35, 83]. One study showed that the onset of active labor is characterized by contractions of 20 to 25 s , while two studies (with the same first author) found that contractions last >40 s [50, 51]. Two studies included additional physiological symptoms in their definition of the onset of active labour: fluid loss  and bloody spectacle [29, 72]. Most studies that defined the onset of the first stage of labour included regular painful contractions in their definition (n = 9.82%) [32-34, 38, 47, 62, 69, 70, 73]. Only one study referred to the duration or frequency of contractions at the onset of labour in the first stage and showed that contractions should last >40 s .