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Updated: Jun 20, 2025

Anogenital Distance and Perineal Measurements of the Pelvic Organ Prolapse POP Quantification System
Published on: September 20, 2018
Obstetric anal sphincter injuries during instrumental vaginal delivery: An observational study based on 18-years of
Kathrine Fodstad1, Katariina Laine2,3, Sari Räisänen4
1Department of Obstetrics and Gynecology, Bærum Hospital, Vestre Viken Hospital Trust, Drammen, Norway.
Objective:
To determine the prevalence and secular trends of obstetric anal sphincter injuries (OASIS) in vacuum and forceps deliveries in Norway, both with and without episiotomy.
Design:
Population-based real-world data collected during 2001-2018.
Setting:
Medical Birth Registry Norway.
Population Or Sample:
Nulliparous women with singleton foetuses in a cephalic presentation delivered by either vacuum or forceps (n = 70 783).
Methods:
Logistic regression analyses were applied to the OASIS prevalence in six 3-year time periods. Both crude odds ratios and adjusted odds ratios (aORs) with 95% confidence intervals (CIs) were determined.
Main Outcome Measures:
OASIS prevalence.
Results:
The OASIS prevalence in vacuum and forceps deliveries decreased from 14.8% during 2001-2003 to 5.2% during 2016-2018. The overall reduction between the first and last 3-year time period was 61% (aOR = 0.39, 95% CIs = 0.35-0.43). The only exception to this decreasing trend in OASIS was found in forceps deliveries performed without an episiotomy. The OASIS prevalence was approximately twofold higher in forceps compared to vacuum deliveries (aOR = 1.92, 95% CIs = 1.79-2.05). Performing either a mediolateral or lateral episiotomy was associated with a 45% decrease in the prevalence of OASIS relative to no episiotomy (aOR = 0.55, 95% CIs = 0.52-0.58).
Conclusions:
Opting for vacuum rather than forceps delivery in conjunction with a mediolateral or lateral episiotomy could significantly lower the OASIS prevalence in nulliparous women.
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