In Rh isoimmunization management, the peak systolic velocity (PSV) of the fetal middle cerebral artery (MCA) on Doppler is used to predict fetal anaemia. A MCA-PSV greater than how many multiples of the median (MoM) indicates the need for fetal blood sampling/intrauterine transfusion?
- A >1.29 MoM
- B >1.5 MoM ✓
- C >2.0 MoM
- D >1.0 MoM (above the median for gestational age)
Correct answer: B. >1.5 MoM
Explanation
The Mari (2000) landmark study established that MCA-PSV >1.5 MoM (multiples of the median for gestational age) has 100% sensitivity for moderate-severe fetal anaemia (haemoglobin >2 SD below mean) and should trigger fetal blood sampling ± intrauterine transfusion. This threshold replaced invasive amniocentesis for optical density (ΔOD450, Liley chart) as the primary surveillance tool for fetal anaemia in Rh isoimmunization.
Reference: Williams Obstetrics, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.