This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
[{'content': 'Sinusoidal heart rate pattern is seen in: \nSelect and explain. \nA. Placenta previa, B. Vasa previa, C. Battledore placenta, D. Succenturiate placenta', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Sinusoidal Pattern:\n\nStable baseline heart rate of 120 to 160 beats/min with regular oscillations.\nAmplitude of 5 to 15 beats/min (rarely greater).\nLong-term variability frequency of 2 to 5 cycles per minute.\nFixed or flat short-term variability.\nOscillation of the sinusoidal waveform above or below a baseline.\nAbsence of accelerations.\n\nCauses of Sinusoidal Pattern:\n\nSerious fetal anemia due to Rh-isoimmunisation/rupture vasa previa / feto maternal hemorrhage / twin to twin transfusion.\nDrugs — Meperidine, morphine, alpha prodine and butorphanol.\nAmnionitis.\nFetal distress (+/–).\nUmbilical cord occlusion.', 'role': 'assistant'}]