BACKGROUND : Escalation in the global rates of labour interventions, particularly cesarean section and oxytocin
augmentation, has renewed interest in a better understanding of natural labour progression.
Methodological advancements in statistical and computational techniques
addressing the limitations of pioneer studies have led to novel findings and triggered a reevaluation
of current labour practices. As part of the World Health Organization's Better Outcomes
in Labour Difficulty (BOLD) project, which aimed to develop a new labour monitoring-to-action tool, we examined the patterns of labour progression as depicted by cervical dilatation
over time in a cohort of women in Nigeria and Uganda who gave birth vaginally following
a spontaneous labour onset.
METHODS AND FINDINGS : This was a prospective, multicentre, cohort study of 5,606 women with singleton, vertex,
term gestation who presented at 6 cm of cervical dilatation following a spontaneous labour
onset that resulted in a vaginal birth with no adverse birth outcomes in 13 hospitals across
Nigeria and Uganda. We independently applied survival analysis and multistate Markov
models to estimate the duration of labour centimetre by centimetre until 10 cm and the
cumulative duration of labour from the cervical dilatation at admission through 10 cm. Multistate
Markov and nonlinear mixed models were separately used to construct average labour
curves. All analyses were conducted according to three parity groups: parity = 0 (n = 2,166),
parity = 1 (n = 1,488), and parity = 2+ (n = 1,952). We performed sensitivity analyses to
assess the impact of oxytocin augmentation on labour progression by re-examining the progression
patterns after excluding women with augmented labours. Labour was augmented
with oxytocin in 40% of nulliparous and 28% of multiparous women. The median time to
advance by 1 cm exceeded 1 hour until 5 cm was reached in both nulliparous and multiparous
women. Based on a 95th percentile threshold, nulliparous women may take up to 7
hours to progress from 4 to 5 cm and over 3 hours to progress from 5 to 6 cm. Median cumulative
duration of labour indicates that nulliparous women admitted at 4 cm, 5 cm, and 6 cm
reached 10 cm within an expected time frame if the dilatation rate was 1 cm/hour, but their corresponding 95th percentiles show that labour could last up to 14, 11, and 9 hours,
respectively. Substantial differences exist between actual plots of labour progression of individual
women and the `average labour curves' derived from study population-level data.
Exclusion of women with augmented labours from the study population resulted in slightly
faster labour progression patterns.
CONCLUSIONS : Cervical dilatation during labour in the slowest-yet-normal women can progress more slowly
than the widely accepted benchmark of 1 cm/hour, irrespective of parity. Interventions to
expedite labour to conform to a cervical dilatation threshold of 1 cm/hour may be inappropriate,
especially when applied before 5 cm in nulliparous and multiparous women. Averaged
labour curves may not truly reflect the variability associated with labour progression, and
their use for decision-making in labour management should be de-emphasized.
S1 STROBE Checklist.
S1 Fig. States and matrix of possible transitions of cervical dilatation. (a) Schematic representation
of possible states from 2 cm to 10 cm of cervical dilatation until birth (absorbing
state). (b) Matrix representation of all possible transitions between states of cervical dilatation.
S2 Fig. 3D graphical illustration of transition (matrix) model. The temporal evolution of
the distribution representing the theoretical cohort entering labour at 2 cm of cervical dilation.
Example of graphical representation of the transition (matrix) model for a simple case study
where each state (2, 3, 4, 5, 6, 7, 8, 10) is modelled as the possible next cervical dilatation until
the delivery state (D). Simulation was for a period cycle of 1 hour between transitions for the
sake of simplicity.
S3 Fig. Average labour curves by parity based on nonlinear mixed models. P0, nulliparous
women; P1, parity = 1 women; P2+, parity = 2+ women.
S1 Video. Individual plots of cervical dilatation, average labour curve (from Markov models),
and alert line for nulliparous women.
S2 Video. Individual plots of cervical dilatation, average labour curves (from Markov models),
and alert line for multiparous women.
S3 Video. Individual plots of cervical dilatation, average labour curve (from nonlinear
mixed models), and alert line for nulliparous women.
S4 Video. Individual plots of cervical dilatation, average labour curves (from nonlinear
mixed models), and alert line for multiparous women.