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Is amniotomy a risk factor for severe perineal trauma? -A Swedish nationwide register study
Sofia Tallhage1,2, Kristofer Årestedt3,4, Kristina Schildmeijer3
1Faculty of Health and Life Sciences, Linnaeus University, Kalmar, 391 82, Sweden. sofia.tallhage@lnu.se.
Background:
Severe perineal trauma (SPT) is a serious complication of vaginal birth with potential physical and psychological consequences. Amniotomy is a commonly used labour intervention with uncertain evidence. A recent Norwegian study suggested a possible association between amniotomy and SPT. The aim of the study was to investigate whether amniotomy is independently associated with SPT, and whether the timing of amniotomy affects the occurrence of SPT in Swedish nulliparous and multiparous women.
Methods:
This nationwide register-based study included 403 342 women who gave birth between 2015 and 2020. Data were obtained from the Swedish Pregnancy Register. The main outcome, SPT, was defined using International Classification of Diseases (ICD-10) diagnosis codes O70.2 and O70.3. Associations were assessed using binary and multiple logistic regression analyses, with adjustment for maternal, obstetric, and neonatal factors.
Results:
The incidence of SPT was 5.1% among nulliparous and 0.9% among multiparous women. In unadjusted analyses, amniotomy was associated with increased odds of SPT in both nulliparous [OR 1.11; 95% CI, 1.07-1.16] and multiparous women [OR 1.13; 95% CI, 1.03-1.23]. However, these associations were not present in adjusted analyses [nulliparous: OR 1.00; 95% CI, 0.95-1.05; multiparous: OR 0.96; 95% CI, 0.86-1.07]. Early amniotomy was associated with a higher prevalence of obstetric interventions, and labour characteristics linked to SPT risk, consistent with confounding by indication. In adjusted analyses, timing of amniotomy was not associated with SPT in multiparous women, while in nulliparous women a longer interval between amniotomy and birth was associated with lower odds of SPT.
Conclusions:
Amniotomy was not independently associated with severe perineal trauma after adjustment for maternal, obstetric, and neonatal factors in this large nationwide cohort. The observed associations with timing likely reflect underlying labour complexity rather than a causal effect. These findings support a cautious and individualised use of amniotomy in clinical practice.
