Risk of Obstetric Anal Sphincter Injuries After Labor Induction Compared to Spontaneous Labor

Thursday, October 5, 2023

11:40 AM – 11:44 AM US PST

Location: B113-116

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Image Label: Characteristics of Women with and without Obstetric Anal Sphincter Injuries

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Image Label: Multivariable Logistic Regression for Obstetric Anal Sphincter Injuries

Presenting Author(s)

Melissa A. Salinas, MD (she/her/hers)

Resident Physician
George Washington University
Arlington, Virginia, United States

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Co-Author(s)

SP

Savita N. Potarazu, MPH (she/her/hers)

Medical Student
George Washington University School of Medicine & Health Sciences
Potomac, Maryland, United States
Sara Rahman, MD (she/her/hers)

Urogyn Fellow
Cleveland Clinic
CLEVELAND HEIGHTS , Ohio, United States
DL

Do H. Lee, MPH(c) (she/her/hers)

Masters in Public Health, Biostatistics (Candidate)
George Washington University
Washington, District of Columbia, United States
LD

Lydia Deaton, B.S. (she/her/hers)

Medical Student
George Washington University School of Medicine and Health Sciences
Washington, District of Columbia, United States
JW

Julia Whitley, MD

Maternal-Fetal Medicine Fellow
Washington University in St. Louis
Saint Louis, Missouri, United States
DH

Devin Hill, B.S.

Medical Student
George Washington University School of Medicine and Health Sciences
1371 Perry Pl NW, District of Columbia, United States
KC

Kharastin Chea-Howard, BS

MD/MPH Candidate
George Washington University
Washington, District of Columbia, United States
CB

Ciara Bryson, B.S.

Medical Student
George Washington University School of Medicine and Health Sciences
Washington, District of Columbia, United States
Charelle M. Carter-Brooks, MD, MSc (she/her/hers)

Assistant Professor Urogynecology, Department of Obstetrics & Gynecology, Department of Urology
George Washington University School of Medicine and Health Sciences
WASHINGTON, District of Columbia, United States

Disclosure(s):

Melissa A. Salinas, MD: No financial relationships to disclose

Savita N. Potarazu, MPH: No financial relationships to disclose

Sara Rahman, MD: No financial relationships to disclose

Do H. Lee, MPH(c): No financial relationships to disclose

Lydia Deaton, B.S.: No financial relationships to disclose

Julia Whitley, MD: No financial relationships to disclose

Devin Hill, B.S.: No financial relationships to disclose

Kharastin Chea-Howard, BS: No financial relationships to disclose

Ciara Bryson, B.S.: No financial relationships to disclose

Charelle M. Carter-Brooks, MD, MSc: No financial relationships to disclose

Objectives: While elective induction of labor (IOL) at 39 weeks decreases primary cesarean section rate, little is known about the effects of IOL on obstetric anal sphincter injury (OASI). Our objective was to evaluate if IOL increased the risk of OASI.

Methods: This is a retrospective case-control study from a single, academic center in an urban setting. This included women with term (37-42 weeks), singleton pregnancies, who had a vaginal delivery from 10/2015 to 12/2021. Individuals with the primary outcome, OASI, were identified and matched 1:4 with controls (no OASI) by delivery date. Multivariable logistic regression was performed to assess for associations between IOL and OASI, while controlling for known risk factors.

Results: A total of 1,409 women were identified. This included 625 (44.4%) women who identified as White, 479(34.0%) Black, 70(5%) Asian, 54(3.3%) Latina/Hispanic, and 181(12.9%) other/unknown. Mean age was 32 years. More women had a gestational age of 37-39 weeks compared to 40-42 weeks (54.9 vs 45.1%).

There were 303(21.5%) OASI: 287(20.4%) third-degree and 16(1.1%) fourth-degree lacerations. Women with OASI were more likely to be White or Asian, and have commercial insurance. They were twice as likely to have thyroid disease and less likely to have gestational hypertension (Table 1). Women with OASI were less likely to have a previous vaginal delivery (9.2% vs 54.2%, p< 0.001) but more likely to have a previous cesarean delivery (CD) (13.9% vs 9.0%, p=0.014). There were no differences in frequency of prior OASI.

Intrapartum factors associated with OASI were gestational age 40-42 weeks (58.1 vs 41.6%, p< 0.001), epidural anesthesia (76.9% vs 60%, p< 0.001), malpresentation (5.6% vs 2.1%, p=.006), operative delivery (32% vs 3.5%, p< 0.001), episiotomy (4% vs 1.4%, p=0.005), and higher birth weight (p < 0.001).

For our primary outcome, we found IOL increased the likelihood of OASI by 49% compared to spontaneous labor (OR 1.49, 95%CI [1.138, 1.949]). However, this association was no longer significant when adjusting for known risk factors for OASI including, race, gestational age, neonatal weight, episiotomy, operative delivery, analgesia use, labor augmentation, pre-eclampsia, history of vaginal delivery, prior CD, and prior third-degree laceration (aOR 1.35, 95%CI [0.910, 1.999], Table 2).

Conclusions: IOL was not associated with OASI when accounting for known antepartum and intrapartum risk factors. Further investigation of modifiable and non-modifiable risks during labor is imperative to decrease the risk of OASI and the associated pelvic floor disorders.