Fetal anemia is diagnosed by which test?

• A. Umbilical venous pH
• B. Fetal MRI
• C. Amniotic fluid bilirubin
• D. MCA Doppler

Answer: (D)

Fetal anemia is most effectively screened with Doppler assessment of the middle cerebral artery, specifically measuring the peak systolic velocity. In an anemic fetus, the blood becomes less viscous and the heart pumps more to compensate, which increases flow velocity in the cerebral circulation. The MCA-PSV is expressed as a multiple of the median for gestational age, and a value around or above 1.5 MoM suggests moderate to severe anemia, prompting further confirmation with fetal blood sampling and consideration of intrauterine transfusion if needed.

Other tests listed aren’t used to diagnose fetal anemia in routine practice. Umbilical venous pH reflects acid-base status at birth rather than anemia. Fetal MRI isn’t a diagnostic tool for anemia. Amniotic fluid bilirubin was used in the past to gauge fetal hemolysis but is invasive and less reliable than MCA Doppler for screening.