PROPENSITY-ID: Sonographic and Clinical Assessment of Head Position Prior to Instrumental Delivery and Labour Outcomes

Plain-language summary

Instrumental delivery is performed in 3-15% of all births (1). Successful instrumental delivery avoids need for cesarean section with associated maternal surgical morbidity, risk from neonatal disimpaction and future pregnancy implications. However, instrumental birth carries risk of maternal perineal and anal sphincter injury, postpartum haemorrhage, shoulder dystocia and fetal trauma (2,3). Additionally, failure of instrumental birth requires delivery by cesarean section with a more deeply impacted fetal head, resulting in compounding of fetal and maternal risks (3,4). Therefore, appropriately identifying women that are at risk of failed instrumental birth is important to reduce maternal and neonatal morbidity. Fetal head position and station are key determinants in success of instrumental birth, traditionally assessed with digital vaginal examination (1,5). There is now high quality evidence showing that intrapartum ultrasound is a more reliable tool in determining fetal head position and station compared to digital vaginal examination (6,7). Additionally, intrapartum ultrasound has been shown to predict outcome of instrumental birth and improve accuracy of instrument placement (8-11). However, no randomised studies to date have demonstrated a benefit in maternal and neonatal morbidity from using intrapartum ultrasound, possibly due to being underpowered. Low recruitment of studies has been suggested to occur due to practitioners electing to use ultrasound rather than randomise participants, despite the absence of evidence supporting clinical benefit (13). This study aims to evaluate whether the assessment of the fetal occiput position by intrapartum sonography before instrumental delivery improves labour outcomes by using an observational design with propensity score matching analysis. This international multicentre prospective observational study will compare outcomes of two parallel groups: * Group 1: patients submitted to instrumental delivery preceded by the use of ultrasound for the assessment of the occiput position by clinicians who routinely perform intrapartum sonography as an adjunct to clinical examination prior to vacuum delivery * Group 2: patients having submitted to instrumental delivery without the adjunct of by clinicians not performing intrapartum sonography prior to vacuum delivery The investigators will perform a propensity score (PS) matching analysis to assess the effect of US as an adjunct to clinical examination prior to instrumental delivery on the occurrence of failed instrumental delivery, adjusting for important differences in baseline characteristics between groups to reduce confounding bias. The investigators will assess two primary outcomes of vaginal delivery and composite adverse perinatal outcome in additional to maternal morbidity and instrumental failure rates.

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