Fetal Anemia (MCA-PSV)

Step-by-step decision

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Full pathway

1. [Decision] MCA-PSV (MoM) + cause + hydrops
   MCA-PSV (MoM) + cause + hydrops? (Anemia → reduced viscosity + raised cardiac output → raised MCA-PSV. Mari: MCA-PSV ≥1.5 MoM predicts moderate-severe anemia (sensitivity 100%, specificity 88%). Measure at the proximal MCA origin, zero angle, no fetal movement. Causes to check: red-cell alloimmunization (maternal antibodies), parvovirus, fetomaternal hemorrhage, alpha-thalassemia, TAPS.)
   • MCA-PSV <1.5 MoM, no hydrops (at risk/under monitoring) → MCA-PSV <1.5 · serial monitoring
   • MCA-PSV ≥1.5 MoM or hydrops present → ≥1.5 MoM/hydrops → intrauterine transfusion
2. [End] MCA-PSV <1.5 · serial monitoring
   MCA-PSV <1.5 MoM, no hydrops: continue serial MCA-PSV monitoring (in alloimmunization from ~16–18 weeks every 1–2 weeks) + maternal antibody titer/paternal antigen zygosity + parvovirus serology/PCR + Kleihauer-Betke; manage by cause and trend.
3. [End] ≥1.5 MoM/hydrops → intrauterine transfusion
   MCA-PSV ≥1.5 MoM or fetal hydrops: suggests moderate-severe anemia; cordocentesis to confirm Hb + intrauterine transfusion (IUT); Kell alloimmunization (suppresses erythropoiesis, mild hemolysis) still monitored by MCA-PSV; parvovirus is often self-limited but severe cases still need IUT; near term may deliver; multidisciplinary.

Source guidelines & references

• Fetal anemia MCA-PSV prediction (Mari NEJM 2000/2002; ≥1.5 MoM)

This pathway is our own synthesis of the decision logic in the guidelines above (not the guideline verbatim); thresholds and workflows change as guidelines update — in practice follow the latest guideline, your institution's protocol and the individual patient.

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