This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diagnosis in obstetrics, Subject name: Gynaecology & Obstetrics
[{'content': 'On Doppler studies which is an ominous sign for IUGR fetus : \nSelect and explain. \nA. Increase S/D ratio, B. Reverse diastolic flow, C. Diastolic notch, D. All of the above', 'role': 'user'}, {'content': "Answer: B \nExplanation: Absence of end-diastolic frequencies or reverse diastolic flow patterns in the umbilical aery usually indicates poor perinatal outcome. Reference: Dutta's Textbook of Obstetrics 7th edition page no 227", 'role': 'assistant'}]