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': 'On doppler the most omnious sign indicating fetal compromise is: \nSelect and explain. \nA. ↑ pulsatality index in umblical art, B. ↑S/D blood flow ratio, C. ↑Cerebral arter flow, D. Absent diastolic flow', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Doppler ultrasound is used to assess the uterine, placental and fetal arterial and venous system.\nIt is especially relevant in IUGR.\n\nRatios measured by Doppler:\n\nS/D – Systolic - diastolic ratio or S/D ratio (most commonly)\nS-D/S – Resistance index\nS-D/Mean – Pulsatility index\n\nUmbilical artery vessels:\n\nBlood flow across the umbilical arteries provides a comprehensive overview of the - fetal blood supply and helps in detecting fetal circulatory compromise.\nThe systolic component of blood flow reflects the cardiac pump and the diastolic component the distal vascular bed.\nIn this case the distal vascular bed is the placental villous tree and hence umbilical artery Doppler is actually a placental and not a fetal Doppler.\nThe umbilical artery is characterised by forward\xa0low resistance flow.\nAs gestation increases, there is gradual fall in all the resistance indices so the amount of forward diastolic flow increases (Remember : Diastolic flow is inversely related to peripheral resistance). systolic/diastolic rates decreases as period of gestation increases.', 'role': 'assistant'}]