Methods: This was a retrospective cohort study at the gynecological ultrasound unit of a tertiary hospital, which included primipara women who performed a pelvic floor ultrasound (US) between January 2012 and January 2020. LAM avulsion was sought by 3D transperineally US, using tomographic imaging of the puborectalis portion of LAM, on the plane of minimal hiatal dimensions. A levator-uretra gap >25mm identified minor or major avulsion. Age, parity, type of delivery, newborn weight, clinical symptoms and history of pelvic surgery were assessed by clinical records. Results: A total of 224 women were included, with median age of 59 (24-90) years. Pelvic prolapse (25,9%) and stress urinary incontinence (18,3%) were the most frequent signs/symptoms. Most women (62%) had an eutocic delivery, followed by forceps (21,4%), Caesarean (11,6%) and vacuum (4,9%) extraction. Avulsion of LAM was detected in 42,8%, however this rate was significantly more frequent with forceps (83,3%), followed by eutocic (36,7%)/vacuum extraction (36,4%) and less frequent in Caesarean section, where this event was almost absent (3,8%; p < 0,001). Globally, the most frequent type of lesion was bilateral major avulsion (13,8%), followed by unilateral major (11,2%) and bilateral minor avulsion (7,1%). A subjective impression of a thinner puborectalis portion was noted in 16% of non-avulsion cases. Unilateral lesions were mainly on right sided of the body (68% vs 32%, p < 0,001). At multivariate logistic regression, age and type of delivery appear independently associated to LAM avulsion (p = 0,026). Conclusions: Our results suggest that, in primipara women, a positive association exists between forceps and LAM avulsion, while Caesarean appears to be protective. The most frequent type of lesion is bilateral major avulsion and right sided unilateral lesions are more frequent than left ones. VP68.11 Diagnostic accuracy of 3D transperineal ultrasound for detecting obstetrical anal sphincter injuries: a systematic review and meta-analysis

3rd trimester ultrasound and birthweight equal or above 30 percentiles. We included singleton-pregnancies with EFW≥p40 on the ultrasound performed in our centre, that delivered after 34 weeks. Electronic fetal monitoring was performed throughout all labour, and whenever asked regional analgesia. The primary outcome was the need of instrumental or Caesarean delivery due to non-reassuring fetal status (NRFS). Secondary outcomes were: neonatal intensive care unit (NICU) admission; Apgar score at 5th minute <7; fetal death or neonatal death. Results: During the study period, 90 cases met the inclusion criteria: 17 cases in the study group and 73 cases in the control group. Median percentile at 3rd trimester ultrasound was 62 (40-98) and birth occurred at 39 (35.4-41.5) weeks. Median percentile at birth was 60 (1-100). Although it was not significantly different, the needed for instrumental or Caesarean delivery for NRFS was higher in the decelerated growth group (p-value 0.451). There were no differences between groups regarding secondary outcomes. Conclusions: In our study, decelerated growth was not associated with adverse perinatal outcomes. The small sample and its retrospective nature are the main limitations of our study. VP36.