Influence of difficulty of instrumentation with vacuum on the rate of levator ani muscle avulsion identified by 3-4d transperineal ultrasound

Objectives: Evaluation of the influence of difficulty of instrumentation with vacuum on the rate of levator ani muscle (LAM) avulsions.Materials and methods: Prospective observational study with 86 nulliparous women with at term gestation who required instrumentation with vacuum to complete fetal extraction. After every delivery, each explorer reported the number of vacuum tractions needed to complete fetal extraction, as well as the subjective complexity of the instrumentation. LAM avulsion rate was assessed by 3D-4D transperineal ultrasound evaluation 6months after delivery.Results: Seventy nine cases were evaluated and classified as either easy delivery (below three vacuum tractions; n=49) or difficult delivery (three or more vacuum tractions; n=30). No differences in obstetric characteristics were observed between study groups, with the following exceptions: fetal head circumference (34.82.7 versus 35.2 +/- 1.1; p=.013) and fetal weight at birth (3260 +/- 421 versus 3500 +/- 421; p=.016). No statistically significant differences between study groups were observed in LAM avulsion rate (36.7 versus 30%) and levator hiatus area (cm(2)) at rest (18.44 +/- 3.95 versus 17.75 +/- 3.90).Conclusions: The number of vacuum tractions needed to complete fetal extraction is not associated to a higher LAM avulsion rate nor with differences in levator hiatus area.