The variety of breech presentation at term is about 3-4% of all births. Our study aims to assess the value of using an equimolar mixture of oxygen and nitrous oxide. Indeed, in some patients algic or relaxed, the success rate seems more important.

It's a single blind prospective randomized controlled study, comparing success rate of ECV after an equimolar mixture of oxygen and nitrous oxide or placebo (medical air).

We need to include 150 patients (75 in each arm), for a period of 2 years. After ECV, we will give the patient a satisfaction questionnaire. We compare the success rate of ECV as primary outcome.

Inclusion Criteria:

• age ≥ 18 years
• pregnancy at term (≥36 weeks)
• singleton foetus in breech or transverse presentation
• acceptance of ECV
• signature of informed consent

Exclusion Criteria:

• contraindications of ECV: placenta praevia, obstacle praevia, multiple pregnancy, foetal death, foetal heart rhythm disorder, lack of amniotic fluid, HIV-positive patient
• contraindications of equimolar mixture of oxygen and nitrous oxide : patient who require pure oxygen ventilation, disorders of consciousness that impede the cooperation of the patient, pneumothorax, pulmonary embolism, ocular surgery