Objective: This study aimed to determine the additional diagnostic information provided by prenatal (fetal) magnetic resonance imaging (pMRI) following tertiary ultrasound (US) for fetal cranial abnormalities in complicated monochorionic gestations. Methods: Women with complicated monochorionic gestations complicated by twin–twin transfusion syndrome, co-twin demise (CD), selective intrauterine growth restriction, and/or twin anaemia–polycythaemia sequence who were referred for pMRI after tertiary US were included. Additional diagnostic information by pMRI that changed prognostic counselling was the primary outcome. Results: Thirty-three women with 48 live fetuses had pMRI at a median of 25 weeks (range: 21–29). Three of ten survivors of spontaneous CD, one of eight survivors of CD after twin–twin transfusion syndrome and 1/30 co-survivors had diagnostic information added by pMRI that altered counselling; US was normal in two and in the other three underrepresented parenchymal injury (5/33 = 15%; 95% confidence interval ±0.27–0.03). Additional findings included occipital lobe infarction, hemispheric injury, dural sinus thrombosis, ischaemia-producing polymicrogyria and intraventricular haemorrhage. Another 8/33 women had additional information provided by pMRI that did not alter counselling. Conclusion: Prenatal magnetic resonance imaging resulted in changed prognostic counselling in 5/33 pregnancies. Evaluation of incorporation of pMRI into routine surveillance of complicated monochorionic gestations is needed.