Introduction: Faecal incontinence is more common in parous women who have had a difficult vaginal delivery. However, the pathophysiology of the injury resulting in faecal incontinence in such women is incompletely understood. This study therefore aimed to compare anal canal and pelvic floor parameters between continent and incontinent women and measure these during pregnancy and after delivery in order to more fully understand the initial insult to the pelvic floor. Methods: Anal manometry and fatigue (using a water-filled microballoon) and pelvic floor strength and fatigue (using an air-filled vaginal probe connected to a Peritron) were measured in 30 primiparous women at booking, end of pregnancy and 6 months post partum. Ten of these women also underwent measurement of pelvis size using ultrasound. A further 61 women, 39 incontinent and 22 continent, also underwent these measurements in order to compare pelvic floor parameters between continent and incontinent women. Results: Voluntary contraction of the external anal sphincter (EAS) was significantly lower 11 weeks post partum than antenatal values (106.5 ± 43.6 cmH2O antenatally vs 75.5 ± 45.6 cmH2O post partum, p < 0.001) but there was no significant difference between antenatal values and those measured 6 months post partum (p = 0.24). Anal fatigue rate was significantly slower 11 weeks post partum (p = 0.001), but by six months post partum the difference is no longer significant (p = 0.053). Pelvic floor muscle (PFM) strength fell with age and was significantly lower in incontinent women (8.97 ± 12.88 cmH2O) than incontinent women (27.17 ± 18.16 cmH2O; p < 0.001). PFM fatigue rate was also significantly slower in incontinent women (p = 0.01). The PFM strength was significantly higher in nulliparous than parous women (p = 0.002) and fatigue rate was faster (p = 0.022). PFM strength (p = 0.006) and fatigue rate (p =0.004) were significantly lower six months post partum when compared with antenatal values. It was shown that pelvis size can be measured using ultrasound and was found to be repeatable, but inaccurate when compared with magnetic resonance imaging. Insufficient numbers were studied to show an effect on pelvic floor function. Conclusion: Vaginal delivery causes impairment of EAS voluntary contraction which appears to have recovered by six months post partum. It also causes impairment of PFM contraction which is persistent at six months post partum. The reduced PFM function seen post partum also occurs in incontinent women, adding to the evidence that childbirth causes the initial insult to the pelvic floor which results in faecal incontinence, either immediately or some years later.