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192: Anti-M isoimmunization: management and outcome at a single institution

      Objective

      To review management strategies and outcomes in gravidas with anti-M alloimmunization over 15 years at The Ohio State University, a period that includes implementation of middle cerebral artery Doppler assessment of patients with elevated antibody titers.

      Study Design

      Data collected from 175 pregnancies found to have anti-M antibodies at The Ohio State University from July 2000 through March 2015 was reviewed retrospectively. Patients with additional red blood cell antibodies were excluded. We analyzed indirect and direct antiglobulin tests (DAT), antibody titers, M antigen genotype status, antepartum course, and perinatal outcome for each patient.

      Results

      Anti-M antibodies were found in 131 women with 176 pregnancies over 15 years. Among those with positive indirect antiglobulin tests, 173 pregnancies had titers below or at 1:4. Only one patient with an initial low titer experienced a more than two-fold increase to a titer of 1:64. Two women underwent amniocentesis; one for a rising titer of 1:64 with elevated MCA Dopplers and one for a titer <1:1 with falsely elevated MCA dopplers. 89 (73%) of the 121 infants tested were positive for the M antigen. Eight infants required phototherapy (Table) and there were no cases of hemolytic disease of the newborn, mild or severe.

      Conclusion

      The incidence of severe hemolytic disease of the newborn due to anti-M is extremely low. We found no cases in our review of 175 pregnancies. If anti-M is detected in pregnancy with a low titer (no more than 1:8) and no history of prior pregnancy complications suggesting a hemolytic process, we recommend no further testing other than an indirect antiglobulin test at 28 weeks to evaluate for emergence of other red blood cell antibodies. We do not recommend monthly titers. However, if the initial titer is elevated, serial titers should be performed, with cordocentesis and possible intrauterine transfusion reserved for rising titers with persistently elevated MCA Doppler peak systolic velocities.
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