Prediction of levator ani muscle avulsion by genital tears after vaginal birth—a prospective observational cohort study

Introduction: Visible birth tears and levator ani muscle (LAM) trauma are common after birth. For the diagnosis of LAM trauma ultrasound evaluation is advisable. As ultrasound equipment and trained personnel are not available everywhere at all times, we aimed to evaluate whether specific overt birth tears are an indicator for LAM trauma. Methods: In a prospective cohort study at our center from March 2017-April 2019, we evaluated vaginal births of nulliparous women with singletons in vertex presentation ≥ 36 + 0 gestational weeks for LAM trauma by translabial ultrasound and for overt birth tears by inspection. We then calculated the association of overt birth tears with complete LAM avulsion. Results: Of 213 women, 23.9% had any kind of LAM trauma, with 14.1% being complete avulsions. In univariate analysis, solely high-grade perineal tears (OASIS) were significantly associated with complete LAM avulsions. Conclusions: Fourteen percent of women suffered a complete LAM avulsion after vaginal birth, with OASIS being the only associated parameter of significance. The occurrence of such trauma might be an indicator for a mismatch between the size of the fetus and the structures of the birth canal, leading to birth trauma. Assessing for LAM trauma by translabial ultrasound in women with OASIS might be worthwhile