Nulliparity, use of epidural analgesia, labour augmentation and instrumental vaginal delivery were more common in women with fear of childbirth and these factors were also associated with longer duration of labour (Tables 1 and 2). After adjustment for these factors as well as other factors associated with labour duration, the association of fear of childbirth with duration of labour was attenuated, but remained statistically significant. The adjusted unstandardised regression coefficient was 0.78 (95% CI 0.20–1.35), which corresponds to a labour 47 minutes longer in women with fear of childbirth compared with women without such fear (Table 2). There was weak evidence that counselling for pregnancy concern was associated with reduced duration of labour (Table 2). Standard residual tests of normality, homoscedasticity, linearity and independence of errors showed that the linear regression model fitted the data well.23
Use of epidural analgesia and parity were the two most important confounding factors (Tables 1 and 2). After adjustment for epidural analgesia and parity only, the unstandardised regression coefficient for the association of fear of childbirth with labour duration was 0.75 (95% CI 0.15–1.35). Both in women with (n = 620) and without (n = 1586) epidural analgesia, the mean duration of labour was longer in women with fear of childbirth (Table 3). In women with epidural analgesia, fear of childbirth remained positively associated with labour duration after adjustment for the other study factors (Table 3). No interactive effect between fear of childbirth and epidural analgesia on labour duration could be estimated (P > 0.05).