This exploratory review aimed to provide empirical evidence on the definitions of labor, the statistical approaches and measures reported in randomized controlled trials (RCTs) and observational studies measuring the duration of labor.
A systematic electronic literature search was conducted using different databases. An extraction form was designed and used to extract relevant data. English, French, and German studies published between 1999 and 2019 have been included. Only RCTs and observational studies analyzing labor duration (or a phase of labor duration) as a primary outcome have been included.
Ninety-two RCTs and 126 observational studies were eligible. No definition of the onset of labor was provided in 21.7% (n = 20) of the RCTs and 23.8% (n = 30) of the observational studies. Mean was the most frequently applied measure of labor duration in the RCTs (89.1%, n = 82), and median in the observational studies (54.8%, n = 69). Most RCTs (83%, n = 76) and observational studies (70.6%, n = 89) analyzed labor duration using a bivariate method, with the t-test being the most frequently applied (45.7% and 27%, respectively). Only 10.8% (n = 10) of the RCTs and 52.4% (n = 66) of the observational studies conducted a multivariable regression: 3 (30%; out of 10) RCTs and 37 (56%; out of 66) observational studies used a time-to-event adapted model.
This survey reports a lack of agreement with respect to how the onset of labor and phases of labor duration are presented. Concerning the statistical approaches, few studies used survival analysis, which is the appropriate statistical framework to analyze time-to-event data.