It is possible to perform a pelvimetry by MRI as a substitute to pelvimetry by CT, hence sparing the patient from a dose of irradiation.

The Principal investigator want to evaluate new MRI sequences offering both an optimal contrast between mineral bone and soft tissues, and a shorter acquisition time. Indeed, the recent developments of specific MRI sequences to preferentially image the mineral bone (namely the ZTE and lavaflex 3D T1-weighted SPGR sequences) allow performing pelvimetry measurements on MR images offering an optimal "pseudo CT" contrast, with an MR acquisition time that is less than 10 minutes. Preliminary tests of these sequences have been carried out in our center in order to be able to implement these sequences on our clinical and research MRI machines. The study team wish to undertake a study to validate the use of this rapid and non-irradiating MRI approach, with the aim to replace a CT pelvimetry by a MRI pelvimetry demonstrated as being as reliable.

Inclusion Criteria:

• Pregnant woman 33 to 41 week
• Woman who gave birth by cesarean section, for whom the obstetrician requests a pelvimetry CT for the next pregnancy
• Pelvimetry planned by the obstetrical team outside of "emergency" pathway
• Adhere to the study protocol after reading the patient information document have signed the informed consent form to participate in the study

Exclusion Criteria:

• Usual contraindications to MRI (Pacemaker, Metallic foreign body, Cochlear implant,…)
• Severe claustrophobia
• uncomfortable back position

having an uterus