Clinical consequences of the extremely rare anti‐PP1Pk isoantibodies in pregnancy: a case series and review of the literature

Background The absence of the red cell antigens P, P1 and P k , known as ‘p’, represents an extremely rare red cell phenotype. Individuals with this phenotype spontaneously form anti‐PP1P k isoantibodies, associated with severe haemolytic transfusion reactions, recurrent spontaneous abortion and haemolytic disease of the fetus and newborn (HDFN). Methods We report a series of four successful pregnancies in three women with anti‐PP1P k isoantibodies, one complicated by HDFN, another by intrauterine growth restriction, all managed supportively. We also review the literature regarding the management of pregnancy involving anti‐PP1P k isoimmunization. Results The literature surrounding anti‐PP1P k in pregnancy is limited to a very small number of case reports. The majority report management with therapeutic plasma exchange (TPE) with or without intravenous immunoglobulin. The relationship between titre and risk of pregnancy loss remains unclear, though a history of recurrent pregnancy loss appears important. Although a positive cord blood direct antiglobulin test is frequently noted, clinically significant HDFN appears uncommon, though possible. Conclusion Early initiation of TPE in high risk patients should be strongly considered. If possible, pregnancies should be managed in a high‐risk obstetric or maternal fetal medicine service. The fetus should be monitored closely with interval fetal ultrasound and middle cerebral artery peak systolic volume Doppler to screen for fetal anaemia. Timely sourcing of compatible blood products is likely to be highly challenging, and both directed and autologous donation should be contemplated where appropriate. The International Red Cell Donor Panel may also provide access to compatible products.