SMFM Consult #8: The Fetus at risk for anemia–diagnosis and management

Publications & Guidelines, Consult Series,

Correction to this Consult: In Figure 2, the box that reads "Induce labor at 38-39 weeks" should read "Induce labor at 37-38 weeks". A revised Figure 2, "Algorithm for clinical management of the red cell alloimmunized pregnancy" can be found here.


  • Hemoglobin value that is more than 2 SD below the mean is diagnostic of fetal anemia.
  • Fetal hematocrit of less than 30% as a cutoff for fetal anemia
  • Mild (MoM 0.83-0.65)
  • Moderate (MoM 0.64-0.55)
  • Severe (MoM < 0.55) 
  • Definitive diagnosis made by fetal blood sampling.
  • Screening is performed with MCA Doppler.
  • Delta optical density 450 to detect fetal anemia is primarily of historic interest or used when MCA not possible (not accurate for anti Kell)


EIFs are seen in 3-5% of normal fetus, with prevalence as high as 30% in fetuses of Asian mothers.



  • A MCA-PSV of greater than 1.5MoM is used as a screening test to identify the severely anemic fetus
  • Sensitivity of 75.5% and a specificity of 90.8% were reported for detecting severe anemia. The use of the MCA-PSV trends (as opposed to a single measurement) may decrease the false-positive rate to less than 5%.
  • Start Screening typically 18-20 weeks of gestation.
  • After 24 weeks of gestation, routine testing is usually done on a weekly basis
  • Titers should be repeated serially every 4 weeks and then more frequently if they are found to be rising or with advancing gestational age
  • Parental assessment and testing are key initial steps.
  • Intrauterine Transfusion (Fresh, CMV negative irradiated and leukodepleted Type O Rh (D) negative blood) for Fetal HCT< 30%
  • [Estimated fetal weight] X [EFW] (grams) X [coefficient (table)] = volume to transfuse
  • The final target hematocrit should be approximately 40-50%.

Last Reaffirmed: Sep 1, 2023

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