Prospective study evaluating the feasibility of shear-wave elastography of the uterus during the third stage of labour and following placental delivery. The investigators hypothesize that the stiffness of the myometrium can be measured by using shear-wave technology. This study involves 30 patients with a healthy pregnancy and spontaneous vaginal delivery. One co-investigator will carry out measurements at the uterine fundus, at three different time points: after fetal delivery, after placental delivery and 30 minutes after placental delivery.

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

Pregnant women

Women above 37 weeks of gestation without known risk factors for postpartum hemorrhage who have vaginal births in our centre will be eligible for this study