Does Intrapartum Fever Increase the Risk of Obstetric Anal Sphincter Injury? New Evidence from a Large Cohort Study

Does Intrapartum Fever Increase the Risk of Obstetric Anal Sphincter Injury? New Evidence from a Large Cohort Study

Obstetric anal sphincter injuries (OASIS) remain one of the most significant complications of vaginal birth. Despite advances in obstetric care, third- and fourth-degree perineal tears continue to contribute to long-term maternal morbidity, including anal incontinence, chronic perineal pain, dyspareunia, and reduced quality of life. Identifying modifiable intrapartum risk factors is therefore a major priority in modern obstetrics.

A recently published study in the International Journal of Gynecology & Obstetrics examined whether intrapartum fever and clinical chorioamnionitis are independently associated with OASIS in women undergoing term vaginal delivery. The findings provide valuable insights into the relationship between maternal inflammation during labor and severe perineal trauma. (AbleSci)

Background

Several established risk factors for OASIS are well recognized:

• Nulliparity

• Operative vaginal delivery

• Fetal macrosomia

• Persistent occiput posterior position

• Prolonged second stage of labor

• Shoulder dystocia

• Midline episiotomy

  
  

However, inflammatory conditions occurring during labor have received comparatively little attention. Maternal fever may arise from infectious causes such as clinical chorioamnionitis or from non-infectious causes including epidural-associated fever. Since fever is frequently accompanied by prolonged labor and repeated vaginal examinations, investigators questioned whether it might also be associated with an increased risk of severe perineal injury. (Nature)

Study Design

The investigators conducted a retrospective cohort study including women with:

• Singleton pregnancy

• Cephalic presentation

• Term gestation

• Vaginal delivery

Women with cesarean delivery, multiple gestations, or preterm births were excluded.

The primary outcome was the occurrence of obstetric anal sphincter injury (third- or fourth-degree perineal tear).

The main exposures evaluated were:

• Intrapartum fever

• Clinical chorioamnionitis

Multivariable logistic regression was used to adjust for known confounding obstetric variables.

Key Findings

The study demonstrated that women who developed intrapartum fever experienced higher rates of OASIS compared with afebrile women. Furthermore, clinical chorioamnionitis also showed an association with increased sphincter injury risk, even after accounting for traditional obstetric risk factors. (AbleSci)

These findings suggest that maternal inflammatory states during labor may represent an additional contributor to severe perineal trauma rather than simply reflecting prolonged or difficult labor.

Why Might Fever Increase OASIS Risk?

Although the study was observational and cannot establish causality, several biological mechanisms are plausible.

1. Prolonged Labor

Women with intrapartum fever often experience prolonged labor, particularly a longer second stage. Extended pressure on the pelvic floor may increase tissue stretch and vulnerability to injury.

2. Tissue Inflammation

Inflammation alters collagen organization, increases tissue edema, and may reduce tissue elasticity. Inflamed perineal tissues could therefore be more susceptible to extensive tearing during delivery.

3. Increased Operative Delivery

Maternal fever frequently prompts obstetric intervention because of concerns regarding fetal wellbeing. Operative vaginal delivery itself is a well-established risk factor for OASIS.

4. Repeated Vaginal Examinations

Clinical chorioamnionitis is often associated with prolonged rupture of membranes and multiple vaginal examinations, both markers of complicated labor.

Together, these factors likely contribute to the observed association.

Clinical Implications

The study has several practical implications for obstetricians and labor ward teams.

Heightened Awareness

Women who develop intrapartum fever may warrant increased vigilance during the second stage of labor.

Careful Perineal Protection

Evidence-based perineal protection techniques should be meticulously applied in febrile patients, particularly when additional OASIS risk factors are present.

Judicious Instrumental Delivery

When operative vaginal delivery becomes necessary, careful assessment of fetal position, operator expertise, and appropriate episiotomy technique remain critical.

Prompt Recognition of Infection

Early diagnosis and treatment of suspected intra-amniotic infection remain important not only for maternal and neonatal outcomes but potentially for reducing severe birth trauma.

Strengths of the Study

Several aspects strengthen the reliability of the findings:

• Large cohort of term vaginal deliveries

• Adjustment for multiple known confounding variables

• Clinically relevant outcomes

• Real-world obstetric population

  
  

Limitations

Like all retrospective studies, certain limitations should be considered.

• Association does not prove causation.

• Residual confounding may still exist.

• Fever may represent a marker of prolonged labor rather than a direct cause of tissue injury.

• Distinguishing infectious fever from epidural-associated fever can be challenging.

  
  

Prospective multicenter studies will be needed to clarify the biological mechanisms involved.

How Does This Fit with Existing Evidence?

Previous literature has consistently identified operative vaginal birth, fetal size, nulliparity, and prolonged labor as major determinants of OASIS. More recent work has also explored prediction models incorporating estimated fetal weight and parity-specific risk factors. This new study adds maternal inflammatory status to the growing list of variables that may influence perineal injury risk. (OBGYN Online Library)

Take-Home Messages

• Obstetric anal sphincter injury remains a significant cause of long-term maternal morbidity.

• Intrapartum fever appears to be associated with an increased risk of OASIS.

• Clinical chorioamnionitis may independently contribute to severe perineal trauma.

• Maternal inflammation should be considered an additional marker of high-risk vaginal delivery.

• Careful intrapartum management, timely recognition of infection, and meticulous perineal protection remain essential to improving maternal outcomes.

• Further prospective research is needed to determine whether preventing or promptly treating intrapartum inflammation can reduce the incidence of obstetric anal sphincter injuries.

  
  

Reference

Mustafa Mikhail S, Abu Shqara R, Ganem N, et al. Associations of intrapartum fever and clinical chorioamnionitis with obstetric anal sphincter injuries in term vaginal deliveries. International Journal of Gynecology & Obstetrics. 2026. DOI: 10.1002/ijgo.71183. (AbleSci)