Interobserver agreement in perineal ultrasound measurement of the anovaginal distance: a methodological study

Anovaginal distance and obstetric anal sphincter injury: a prospective observational study

INTRODUCTION AND HYPOTHESIS

No measurements are available for diagnosing the extent of obstetric lacerations. The primary aim of this study was to evaluate the relation between the anovaginal distance (AVD) measured with transperineal ultrasound immediately after delivery and external anal sphincter injury. A secondary aim was to assess whether the palpated perineal thickness was associated with the AVD.

METHODS

A prospective observational study of 150 primiparous women at the University Hospital, Linköping, Sweden. After vaginal delivery, initial inspection and palpation of the perineal thickness were performed by the midwife. The women were then divided into subgroups depending on the degree of the suspected perineal laceration. Transperineal ultrasound of the AVD was performed by a physician. Diagnostics of the perineal laceration were done according to standard care.

RESULTS

Women with an external sphincter injury had a shorter AVD and shorter palpatory perineal thickness compared with women without anal sphincter injury. No external sphincter injuries were diagnosed when the AVD and/or palpation height was > 20 mm. The mean AVD in the group with probable second-degree laceration (n = 85) was 18.8 mm (95% CI 17.8-19.8), in suspected third-degree laceration (n = 33) 15.7 mm (95% CI 13.7-17.7) and in probable third-degree laceration (n = 32) 11.8 mm (95% CI 9.7-13.9) (p < 0.001).

CONCLUSIONS

A short AVD could be a warning sign postpartum and should increase the awareness of possible external sphincter injury before suturing. An AVD of 20 mm seems to indicate a cutoff level of the occurrence of external sphincter injury, but this needs further evaluation.

Maternal Body Mass Index and Anovaginal Distance in Active Phase of Term Labor

Introduction

To evaluate if there was a difference in the anovaginal distance (AVD) measured by transperineal ultrasound between obese and normal weight women.

Material and Methods

A prospective observational study including 207 primiparous women at term in first stage of labor. Transperineal ultrasound with a vaginal probe was used to measure the AVD. Maternal, pregnancy, and delivery characteristics potentially associated with perineal thickness were extracted from woman's medical records. The participants were divided into three BMI groups based on maternal weight in early pregnancy: normal weight (BMI < 25), overweight (BMI 25–29.9), and obesity (BMI ≥ 30). Obese and overweight women were compared with normal weight women regarding the AVD.

Results

The mean AVD was 24.3, 24.9, and 27.0 mm in the normal weight, overweight, and obesity group, respectively. There were no group differences in background characteristics. The AVD was significantly longer in obese women compared with normal weight women (p = 0.018).

Conclusions

The observed longer AVD in obese women might be protective of the anal sphincter complex, explaining lower rates of anal sphincter injuries in this group. Further studies are indicated to evaluate whether the length of the AVD plays a role in the risk assessment of obstetric anal sphincter injury. The trial is registered in ClinicalTrials.gov and the trial registration ID is NCT03149965.