['Relaxation of pelvic ligaments may facilitate parturition in certain animal species. Biomechanical properties of pelvic connective tissue may also influence progress of labour in the human female. This study was designed to test whether peripheral joint mobility or pelvic organ mobility as measures of connective tissue biomechanical properties are associated with progress in labour and delivery mode.', 'Prospective clinical observational study.', 'Tertiary obstetric service.', '200 nulliparous women recruited in antenatal clinic.', 'Translabial ultrasound was used to obtain data on third trimester pelvic organ mobility. Upper limb joint mobility was assessed clinically.', 'Gestational length, length of first and second stage of labour, delivery mode.', 'Pelvic organ mobility was significantly associated with total length of second stage (P = 0.034 to P = 0.002). This was mainly due to the length of passive, not active second stage. There also was a statistically significant association between delivery mode and pelvic organ descent (P = 0.007 to P = 0.001), with the lowest mobility seen in women who required a Caesarean section in second stage. Joint mobility did not correlate with delivery data.'] Is antenatal pelvic organ mobility associated with delivery mode?