Is Amniotomy a Risk Factor for Severe Perineal Trauma? -A Swedish Nationwide Register Study

Abstract

Background: Severe perineal trauma (SPT) is a serious complication with vaginal births, potentially leading to physical and psychological consequences for the woman. Amniotomy is a commonly used labour intervention with uncertain evidence. It was identified as a previously unrecognized risk factor for SPT in a recent Norwegian study. The aim of the thus study was therefore, to investigate whether amniotomy is a risk factor for SPT, and to examine whether the timing of performing amniotomy affects the occurrence of SPT in Swedish nulliparous and multiparous women. Methods: This nationwide register-based study included 477 321 women who had given birth in 2017–2020. Data were collected from the Swedish Pregnancy Register in which most data is collected via direct transfer from medical records. The main outcome, SPT, was identified in the data by International Classification of Diseases (ICD-10) diagnosis codes O70.2 and O70.3. Multiple binary logistic regression analysis was used to estimate odds ratios, adjusted for other risk factors. Results: The incidence of SPT in nulliparous was 5.1% and in multiparous women 0.9%. SPT was more common in both nulliparous and multiparous women who underwent amniotomy. Amniotomy increased the odds for SPT in the simple binary regression analysis for both nulliparous [OR 1.33; 95% CI, 1.28-1.38] and multiparous women [OR 1.12; 95% CI, 1.03-1.22]. This significance was lost in both nulliparous [OR 0.96; 95% CI, 0.87-1.07] and multiparous women [OR 0.83; 95% CI, 0.67-1.03] when analysed in the multiple binary logistic regression. An increasing duration between amniotomy and birth decreased the odds for SPT in nulliparous women. No association was found regarding the timing of amniotomy of occurrence of SPT in multiparous women. Conclusions: SPT was more common in women who underwent amniotomy, however, when adjusted for other risk factors, amniotomy was not identified as a risk factor for SPT. Performing amniotomy near the birth in nulliparous women entailed an increased risk for SPT, indicating the importance of a controlled and slow birth of the baby, to prevent the severe complication of SPT.