The correlation between the type of forceps application and the rate of levator ani muscle avulsion: A prospective cohort study

Objectives: The association between the use of forceps and levator ani muscle (LAM) avulsion seems to be clear-cut. However, whether the lesion is due to the mechanical trauma yielded by the instrument or to the intrinsic complexity of this type of delivery, is yet to be determined. This study aims at determining the difference in LAM avulsion rate between Kielland rotational forceps and non-rotational forceps.

Study design: Prospective observational study with 94 nulliparous women with forceps-assisted deliveries (FD) between July 2015 and January 2016. 3D-TpUS was performed 6 months after every patient's delivery, during which LAM avulsion, and levator hiatus area and anteroposterior and transverse diameters were assessed.

Results: A total of 89 nulliparous were studied, comprising 27 rotational-FD, and 62 non-rotational-FD. No differences in obstetric, intrapartum, or neonatal characteristics were observed between study groups. There were no statistically significant differences in the presence of avulsion between cases of rotational forceps (44.4% vs 35.5%, OR: 1.5 [0.6-3.6]), correction of asinclitism of the fetal head (34.4% vs. 40.4% OR: 0.8 [0.3-1.9]) or station (midforceps: 32.8% vs low forceps: 50.0% OR: 2.0 [0.8-5.1]).

Conclusions: We have not observed differences in the LAM-avulsion rate between rotational forceps and non-rotational forceps performed by highly experienced personnel in instrumental deliveries.