The effect of replacing vacuum with forceps in operative vaginal delivery: an observational study


Introduction and hypothesis

An increase in vaginal delivery with forceps may increase rates of pelvic floor trauma. This study was designed to predict trauma rates resulting from policies preferencing forceps.


This is an observational cohort study utilizing data from 660 primiparae enrolled in an RCT in two tertiary obstetric units in Sydney, Australia. Participants were assessed clinically and with 4D translabial ultrasound in the late third trimester and again at 3–6 months postpartum. Incidence of trauma associated with mode of delivery was adjusted to reflect change associated with a conversion of vacuum to forceps delivery. Primary outcome measures were third-/fourth-degree tear, levator avulsion (LA) and external anal sphincter (EAS) trauma diagnosed sonographically.


Five hundred four women were seen at a mean of 5.1 (2.3–24.3) months postpartum. After exclusion of 21 because of missing data, 483 women were analysed: 112 (23%) had a CS, 268 (55%) a normal vaginal delivery (NVD), 69 (14%) a vacuum (VD) and 34 (7%) a forceps (FD). One hundred fifty-two women had EAS trauma and/or LA; 17 sustained both. After VD, 32/69 (46%) women suffered LA and/or EAS trauma; after FD, it was 33/34 (97%). Converting VD to FD was estimated to result in an increase in trauma from 152/483 (31%) to 187/483 (39%). A formula can be generated based on local obstetric and ultrasound data to estimate trauma incidence.


A change in obstetric practice resulting in the conversion of primary VD to primary FD would be expected to substantially increase the likelihood of pelvic floor trauma.

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Fig. 1
Fig. 2



Standard deviation


Body mass index


Caesarean section


Normal vaginal delivery


Vacuum delivery


Forceps delivery


Pelvic organ prolapse


Obstetric anal sphincter injury


Pelvic floor muscle contraction




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No funding was received for this study.

Author information




J Caudwell-Hall: Data collection and analysis, manuscript writing/editing.

C Shek: Data collection, manuscript editing.

S Langer: Data collection, Research Midwife.

HP Dietz: Project development, data collection and analysis, manuscript editing.

Corresponding author

Correspondence to Hans Peter Dietz.

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Conflict of interest

Prof. H.P. Dietz and C. Shek have received unrestricted educational grants from GE Medical. The other authors have no potential conflict of interest to declare.

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Caudwell Hall, J., Shek, C., Langer, S. et al. The effect of replacing vacuum with forceps in operative vaginal delivery: an observational study. Int Urogynecol J (2020).

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  • Levator avulsion
  • Birth trauma
  • Forceps
  • Urogynaecology
  • Pelvic organ prolapse
  • Ultrasound