The behaviour of pelvic floor muscles during uterine contractions in spontaneous and oxytocin-induced labour.

Term pregnant women were divided into oxytocin infusion and control groups. The electrical activities of pelvic floor muscles (PFM) were recorded at rest and during contractions electromyographically. The beginning and the end of each contraction were marked on the recorded electromyographic trace. A trace was regarded as 'negative' if no increase in electrical activity was observed and 'positive' if increased electrical activity was observed during the contractions. To evaluate the relative frequency of the areas of electrical activity during uterine contractions (UC) a 'positive electrical activity percentage' was used and calculated as: (total count of positive electrical activity areas)/(total count of UC) × 100. Positive and negative electrical activity percentages were compared. The percentages were significantly different between the groups (p <.01). Positive traces increased in 56.1 and 18.8% in study and control groups, respectively, (p < .01). Multiparous women showed more positive traces than nulliparous women, both in oxytocin-treated and spontaneous labour groups (p < .01). The rate of performed episiotomies was higher in the oxytocin-infused labours (p = .01). During physiological labour contractions the predominant behaviour of PFM seemed to be a relative silent status compared to a more contractile status caused by oxytocin administration. Contracted muscles may produce a counterpressure against expulsive UC leading to obstetrical injuries of these muscles and clinically higher rates in episiotomy decisions. This is the first report of behaviour of PFM during labour contractions and further prospective studies are needed to assess the role of oxytocin administration on PFM and associated clinical consequences. Impact statement What is already known on this subject? The physiological functions of pelvic floor muscles depend on the coordinated actions of these muscles and rely also on unique interactions between the somatic and autonomic nervous systems. Oxytocin is commonly used for the induction and augmentation of uterine contractions and such an induced labour may be more painful for the woman. What do the results of this study add? Pelvic floor muscles tend to contract more frequently during uterine contractions as labour progresses. This difference was more pronounced in labours which were treated with oxytocin infusion. What are the implications of these findings for clinical practice and/or further research? This is the first report of electrophysiological behaviour of pelvic floor muscles during labour contractions in spontaneous and oxytocin-induced labour. Oxytocin administration seems to interfere with the coordination of uterine and pelvic floor muscle contractions. This study may be of interest for researchers to investigate the effect of the worldwide liberal use of oxytocin for induction of labour on pelvic floor muscle damage during parturition.