FMH is not only caused by Rh-D status, and can happen in many infants regardless of blood type compatibility. Even though it may not change the management of future pregnancies it may shed light into the reasons for fetal demise.

If a woman is indeed RhD-negative and has FMH, then it increases the risk for subsequent Rh-isommunization and hemolytic disease in future pregnancies.

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Rh isoimmunization is the most common cause of FMH but other minor blood group variants are also responsible in some cases and unlike Rh isoimmunization, these uncommon incompatibilities often lead to affection of the fetus in first pregnancy. Even in some cases like Kel antigen immunization, fetal RBC precursors may also be affected leading to fetal aplastic anaemia (beside conventional hemolytic anaemia). So, KB test should be done in all women irrespective of Rh status.