Prediction of Uterine Atony After Vaginal Delivery by Elastography

Inclusion Criteria: * singleton pregnancy * cephalic presentation * maternal age \> 18 years old * nulliparous * healthy uncomplicated pregnancy * gestational age between 37-42 weeks of gestation * spontaneous labour and delivery * uncomplicated progression of labour (cervical dilatation at \>1 cm/h) * administration of less than 3 units of oxytocin during the second stage of labour * patient having read, accepted and signed the consent form Exclusion Criteria: * antepartum hemorrhage in the present pregnancy * protracted second stage of labour (more than two hours from full dilatation to delivery) * more than 30 minutes of active pushing * BMI \> 35 kg/m2 * distance from skin to uterus \> 8 cm * age \> 35 years old * instrumental deliveries * bleeding disorders * polyhydramnios * diabetes * pre-eclampsia * high blood pressure * use of anticoagulant medications * clinical chorioamnionitis * placental abnormality (low-lying or abruption) * fetal macrosomia * uterine fibroids * uterine anomalies * previous uterine scar * multiple pregnancy * placental retention * inability to follow procedures or insufficient knowledge of project language * inability to give consent * refusal to participate