Abstract: Objective  To compare the diagnostic efficacy of magnetic resonance imaging(MRI), ultrasound and MRI combined with ultrasound in the diagnosis of type Ⅱ fetal osteogenesis imperfecta(OI) type Ⅱ, so as to explore the application value of MRI combined with ultrasound in the diagnosis of fetal OI typeⅡ. 
Methods  A retrospective analysis was performed on clinical data and imaging data of 18 patients with fetal OI type Ⅱdiagnosed during antenatal examination and confirmed by postoperative pathological examination. With pathology of induction of labor as the gold standard, sensitivity, specificity, accuracy, positive predictive value, negative predictive value of ultrasound, MRI, and ultrasound combined with MRI in the diagnosis of fetal OI were calculated and compared. 
Results  Accuracy of MRI, ultrasound and ultrasound combined with MRI in the diagnosis of fetal OI was confirmed in 11 cases, 15 cases, and 17 cases, respectively.  The diagnostic sensitivity of ultrasound was 61.11%, and the accuracy was 78.00%. The diagnostic sensitivity of MRI was 83.33%, with an accuracy of 90.00%. Considering ultrasound examination results and MRI findings, diagnostic sensitivity and accuracy of ultrasound combined with MRI increased to 94.44% and 96.00% respectively, as compared with ultrasound. 
Conclusion  Fetal MRI combined with ultrasound can improve the diagnostic sensitivity and accuracy of current ultrasonography, which is helpful to guide clinical practice.

Key words: osteogenesis imperfecta, magnetic resonance imaging, ultrasonography