In monitoring Rh-alloimmunised pregnancies, the middle cerebral artery peak systolic velocity (MCA-PSV) >1.5 MoM predicts fetal anaemia with what sensitivity and has replaced which older invasive procedure?

• A Sensitivity ~95%; replaced fetal blood sampling (cordocentesis) as first-line monitoring
• B Sensitivity ~70%; replaced spectrophotometric amniotic fluid analysis (Liley zones)
• C Sensitivity ~80%; replaced maternal serum anti-D titre monitoring
• D Sensitivity ~88%; replaced amniocentesis for bilirubin (ΔOD450 measurement) ✓

Explanation

MCA-PSV >1.5 MoM has ~88% sensitivity for predicting moderate-to-severe fetal anaemia. It has replaced amniocentesis for ΔOD450 (Liley curve analysis), which was the earlier non-invasive monitoring technique. If MCA-PSV >1.5 MoM, cordocentesis (fetal blood sampling) is performed to confirm anaemia and perform intrauterine transfusion if haematocrit <30%. MCA-PSV utilises the physiological principle that anaemic fetuses have increased cardiac output and decreased blood viscosity, resulting in higher velocity flow in the MCA — this can be detected by Doppler as early as 18 weeks.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.