The study was terminated prematurely, as the inclusion period ended on 11/27/2024. Of the 103 patients planned, 77 were included.

The aims of this study are:

• To assess the performance of third-trimester ultrasound scan in the localization of intestinal structures (small bowel, gut, mesenteric vessels..) involved in malrotations with a higher-risk of volvulus compared to a gold standard based on fetal magnetic resonance imaging (MRI).
• To describe normal meconium progression (ultrasound and MRI), prenatal anatomical variants of the fetal digestive tract, and interobserver agreement on prenatal ultrasound.

Introduction: Intestinal malrotation is a rare congenital anomaly resulting from abnormal rotation and fixation of the intestine during embryonic development. It is rarely asymptomatic and most often presents in the neonatal period with obstructive complications, including duodenal obstruction and, most critically, midgut volvulus. Midgut volvulus constitutes a surgical emergency due to the risk of extensive intestinal ischemia and necrosis, which may lead to short bowel syndrome or death.

Currently, there is no prenatal screening strategy for intestinal malrotation, and the feasibility and diagnostic performance of third-trimester obstetric ultrasound for detecting intestinal malrotation have never been formally evaluated.

Aim: To evaluate the diagnostic performance of third-trimester obstetric ultrasound in identifying the intestinal structures involved in high-risk intestinal malrotation associated with volvulus, using fetal MRI as the reference standard.

Methods : Eligible pregnant women will be identified during routine obstetric follow-up at Nîmes or Montpellier University Hospitals and enrolled exclusively in Montpellier. Each participant will undergo a third-trimester obstetric ultrasound and fetal MRI on the same day. Examinations will be performed independently by a senior obstetrician and a senior pediatric radiologist, both blinded to the other modality. Ultrasound visualization of mesenteric vessels, small bowel, and cecum will be compared with fetal MRI findings as the reference standard. Interobserver agreement for ultrasound interpretation will be assessed, and analyses will be stratified by gestational age. Participation duration is one day.

Inclusion Criteria:

• Pregnant women over the age of 18
• Good understanding of French
• Gestational age greater than or equal than 31 weeks
• Fetal MRI indication validated in multidisciplinary staff at weekly meetings of the Multidisciplinary Prenatal Diagnosis Center in Montpellier or Nimes
• Affiliation or beneficiary of a social security scheme
• Declaration of free and enlightened opposition

Exclusion Criteria:

• Complex fetal abdominal malformations responsible for difficult interpretation of imaging: heterotaxis with asplenia or polysplenium, diaphragmatic hernia, omphalocele, gastroschisis, digestive pathology, abdominal tumor, bladder exstrophy or megavessia.
• Fetal chromosomal abnormality
• Request for termination of pregnancy validated by a Multidisciplinary Pre-natal Diagnosis Center

Pregnant women with normal intestinal structure and requiring a fetal MRI for other reason