The fetal middle cerebral artery (MCA) peak systolic velocity (PSV) is used to screen for fetal anaemia in Rh-sensitised pregnancies. The threshold PSV value that indicates moderate-to-severe fetal anaemia and warrants cordocentesis or intrauterine transfusion is:
- A MCA-PSV > 1.5 multiples of the median (MoM) for gestational age ✓
- B MCA-PSV > 1.0 MoM
- C MCA-PSV > 2.0 MoM
- D MCA-PSV > 1.25 MoM
Correct answer: A. MCA-PSV > 1.5 multiples of the median (MoM) for gestational age
Explanation
The Mari criteria (validated in NEJM 2000) established that an MCA-PSV > 1.5 MoM for gestational age has a sensitivity of 100% for detecting moderate-to-severe fetal anaemia. Anaemic fetuses have increased cardiac output and reduced blood viscosity, resulting in faster blood flow detected by Doppler. When MCA-PSV exceeds 1.5 MoM, cordocentesis and intrauterine transfusion are considered. Values between 1.0 and 1.5 MoM are monitored more closely; > 2.0 MoM is not a recognised additional threshold.
Reference: Williams Obstetrics, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.