A comparable rate of levator ani muscle injury in operative vaginal delivery (forceps and vacuum) according to the characteristics of the instrumentation

Abstract

Abbreviations: CI, confidence interval; LAM, levator ani muscle; OR, odds ratio. AbstractIntroduction: Forceps delivery is associated with a high rate of levator ani muscle (LAM) trauma (avulsion) at 35%-65% whereas data on avulsion rates after vacuum delivery vary greatly. Nevertheless, a common characteristic of all previous studies carried out to evaluate the association between instrumental deliveries (forceps and vacuum) and LAM avulsion, is the fact that characteristics of the instrumentation have not been described or evaluated. The objective of this study is to compare the rate of LAM avulsion between forceps and vacuum deliveries according to the characteristics of the instrumentation. Material and methods: Prospective, observational study, including 263 nulliparous women, who underwent an instrumental delivery with either Malmström vacuum or Kielland forceps. The characteristics of the instrumentation, position (anterior position and other position) and height of the fetal head at the moment of instrumentation (low instrumentation [vertex at +2 station] and mid-instrumentation [head isinvolved but leading part above +2 station]) were assessed. Evaluation of LAM avulsion was performed at 6 months postpartum by three-/four-dimensional transperineal ultrasound. Using the multi-view mode, a complete avulsion was diagnosed when the abnormal muscle insertion was identified in all three central slices, that is, in the plane of minimal hiatal dimensions and the 2.5-mm and 5.0-mm slices cranial to this one. To detect a 30% or 15% difference in the LAM injury rate, with 80% power and 5% α-error, we needed, respectively 42 and 99 women per study group.Results: In all, 263 nulliparous individuals have been evaluated (162 vacuum deliveries, 101 forceps deliveries). Instrumentation in an occipito-anterior position was more frequent in vacuum deliveries (75.3% vs 56.4%, P = .002), whereas other positions were more frequent in the forceps deliveries group (24.7% vs 43.6%). No statistically significant differences were noted regarding the height of the fetal head at the moment of instrumentation. No statistically significant differences were found in the presence of LAM avulsion (41.4% vs 38.6%) between vacuum and forceps deliveries.The univariate analysis of the crude odds ratio was 1.17, 95% CI 0.67-1.98, P = .70 for

Influence of the disengagement of the forceps on levator ani muscle injuries in instrumental delivery: A multicenter study

“…We believe that the application of forceps cannot be simplified in this way. In fact, different conditions might influence avulsion in labor, such as the additional space occupied by the branches of the forceps, the increase in the speed of LAM distension, and the greater force required by these deliveries . The 3‐ and 4‐dimensional transperineal ultrasound is an adequate method of evaluation of the pelvic floor musculature because it presents an adequate intra‐class correlation coefficient (0.97) in relation to magnetic resonance and also has very good interobserver correlation (0.61‐0.93) .…”

“…In our study of the disengagement of the forceps, we analyzed the space factor added by the forceps during instrumentation, and observed that an increase in this space is not related to a significant increase in the rate of LAM avulsions when forceps are used without disengagement. In vitro studies have concluded that the risk of avulsion from forceps is not completely explained by the increase in space during delivery . Additionally, it has been reported that maternal complication rates vary widely and depend on several factors that are not independent.…”

“…In fact, different conditions might influence avulsion in labor, such as the additional space occupied by the branches of the forceps, the increase in the speed of LAM distension, and the greater force required by these deliveries. 22,23 The 3-and 4-dimensional transperineal ultrasound is an adequate method of evaluation of the pelvic floor musculature because it presents an adequate intra-class correlation coefficient (0.97) 24 in relation to magnetic resonance and also has very good interobserver correlation (0.61-0.93). 25 In our study of the disengagement of the forceps, we analyzed the space factor added by the forceps during instrumentation, and observed that an increase in this space is not related to a significant increase in the rate of LAM avulsions when forceps are used without disengagement.…”

“…In vitro studies have concluded that the risk of avulsion from forceps is not completely explained by the increase in space during delivery. 22,23 Additionally, it has been reported that maternal complication rates vary widely and depend on several factors that are not independent. These factors include type of instrument used, head position at application, station, indication for intervention, and operator experience.…”

Prevalence of levator hiatal overdistension after vacuum and forceps deliveries

“…A recent study found an adjusted odds ratio (OR) of 0.90 (95% confidence interval [CI]: 0.53, 1.55) for LAM avulsion in vacuum and forceps deliveries, with P = .71. 6 In addition to avulsion, another type of injury causes an increase in the distensibility of the levator hiatus, defined as ballooning 7 or microtrauma (irreversible overdistention). 2 Hiatal overdistention can occur after vaginal delivery and is observed for 19% to 33% 2,8-10 of vaginal births.…”