Question:medium
In modern obstetrics, for a sensitized Rh-negative mother, what is preferred to evaluate the fetal condition?
In modern obstetrics, for a sensitized Rh-negative mother, what is preferred to evaluate the fetal condition?
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Anaemic blood is thinner and flows faster: which vessel velocity captures that non-invasively?
Updated On: Jun 23, 2026
- MCA Doppler peak systolic velocity
- Fetal blood sampling
- Amniocentesis
- Biophysical profile
Show Solution
The Correct Option is A
Solution and Explanation
Concept first: a sensitized Rh-negative pregnancy is at risk of fetal haemolytic anaemia, and the modern way to track that anaemia without entering the uterus is MCA-PSV Doppler.
The physics: anaemic fetal blood has low viscosity and a high-output state, so it streams faster through the middle cerebral artery. A peak systolic velocity above 1.5 MoM for the gestational age flags moderate to severe anaemia and signals the need for cordocentesis and intrauterine transfusion.
Why not the rest: fetal blood sampling (option 2) and amniocentesis (option 3) are invasive and carry procedure risk, so they are no longer the screening tool of choice and have largely been replaced by serial MCA Doppler. Biophysical profile (option 4) grades overall fetal wellbeing and does not specifically detect anaemia.
So the preferred evaluation is MCA Doppler PSV. Ref: Dutta Obstetrics.
The physics: anaemic fetal blood has low viscosity and a high-output state, so it streams faster through the middle cerebral artery. A peak systolic velocity above 1.5 MoM for the gestational age flags moderate to severe anaemia and signals the need for cordocentesis and intrauterine transfusion.
Why not the rest: fetal blood sampling (option 2) and amniocentesis (option 3) are invasive and carry procedure risk, so they are no longer the screening tool of choice and have largely been replaced by serial MCA Doppler. Biophysical profile (option 4) grades overall fetal wellbeing and does not specifically detect anaemia.
So the preferred evaluation is MCA Doppler PSV. Ref: Dutta Obstetrics.
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