Association between levator ani muscle avulsions and technique of vacuum extraction – a prospective exploratory study

AIMS OF THE STUDY Trauma of the levator ani muscle in the form of partial or complete avulsions is common after vaginal births, especially after vaginal-operative births. As there is little information available regarding associations between the technique of vaginal-operative births and levator ani muscle trauma, we aimed to evaluate the association between the process of vacuum extraction and the occurrence of levator ani muscle trauma. METHODS As part of a prospective cohort study at the University Hospital of Zurich between March 2017 and April 2019, we sub-analysed vacuum extractions in nulliparous women with singletons in vertex presentation ≥36+0 gestational weeks. We evaluated their pelvic floor for partial and complete levator ani muscle avulsions using translabial ultrasound 6–10 weeks postpartum and calculated the association of the vacuum procedure itself, along with other fetal, maternal and obstetrical characteristics, with levator ani muscle trauma. RESULTS Levator ani muscle trauma was present in 17 (34.7%) out of 49 women. There were no associations between the different factors evaluated and levator ani muscle trauma in vacuum-assisted births, except that the levator ani muscle group had insufficient uterine contractions. CONCLUSIONS We found no fetal, maternal or obstetrical characteristics or parameters of vacuum technique that were associated with the occurrence of levator ani muscle trauma after vacuum extraction, except for insufficient uterine contractions. Nevertheless, there might be influencing factors that have not yet been evaluated, or are not easily accessible for evaluation, like the adaptations of the fetus inside the birth canal and within the hiatus of the levator ani muscle, and the adaptations of the birth canal to the fetus passing through. This should be the subject of further research with a sample size adequately powered to answer this question properly. (Trial registration number: BASEC-Nr.2016-00908.