26 Risk of obstetric anal sphincter injury by delivering provider type

Abstract

Obstetric anal sphincter injuries (OASIs) have significant short- and long-term effects including pain, anal incontinence, and sexual dysfunction. OASI is one of the few modifiable risk factors for anal incontinence, yet OASI complicate at least 8% of vaginal deliveries. There is a paucity of data examining delivering provider type as a risk factor. Our objective was to assess if the primary delivering provider, certified nurse-midwife versus physician obstetrician, is associated with OASI. We hypothesized more OASIs with midwives as the delivering provider. This was a secondary analysis of a multi-center, retrospective cohort study from the Consortium of Safe Labor. Included were nulliparous women who had a vaginal delivery of a singleton fetus at >37 weeks gestational age from 2002 to 2008. Women were excluded if delivery was complicated by shoulder dystocia or from sites without deliveries. Student t-tests, chi-squared analysis, and Fisher's exact test were used as appropriate to assess baseline characteristics, labor factors, and OASIs. Multivariable logistic regression and propensity score matching analyses were performed to control for characteristics associated with OASI. Data are presented as adjusted odds ratio (aOR). Of 228,668 births at 19 sites, a total of 2,735 births from 3 sites met inclusion criteria: 1,551 physician and 1,184 midwife births. Of all births, 4.24% (n = 116) were complicated by OASI. Physician patients were older (23 ± 5 vs 21 ± 4 years), there were more White patients (26.4% vs 14.3%), privately insured (39.1% vs 22.8%), with higher pre-pregnancy BMI (25.5 ± 6.4 vs 24.8 ± 5.8 kg/m2), more medical co-morbidities, labor inductions (40.9% vs 20.4%), labor augmentations (28.2% vs 16.2%), and episiotomies (15.5% vs 5.2%; all P < 0.05). Midwife patients had higher fetal gestational age (39.7 ± 1.1 vs 39.4 ± 1.2 weeks) and infant birth weights (3.3 ± 0.4 vs 3.2 ± 0.4 kg; all P < 0.05). OASIs were more common in physician compared to midwife births (5.9% vs 2.0%, P < 0.0001). This difference persisted on multivariable logistic regression with OASIs being 2.39 (95% CI = 1.5-3.9) times more likely with physician delivery when controlling for maternal history of heart disease (aOR = 3.9, 95% CI = 1.03-14.6), episiotomy (aOR = 3.1, 95% CI = 2.0-4.9), increasing maternal age (aOR = 1.08, 95% CI = 1.04-1.1), decreasing maternal BMI (aOR = 0.95, 95% CI = 0.92-0.99), non-White race (aOR = 0.61, 95% CI = 0.4-0.96), and increasing birthweight (aOR = 1.03, 95% CI = 1.02-1.05). Area under the curve for this model was 0.78 indicating strong predictive ability. With propensity score matching, OASIs remained higher amongst physicians compared to midwives (6.6% vs 1.8%, P < 0.0001) with an aOR of 3.8 (95% CI = 2.0-7.1). OASIs were more common in physician compared to midwife deliveries even when controlling for other associated factors. Our model may be used as a pre-delivery tool to guide providers on OASIs risk and possible reduction strategies.