Anti-M isoimmunization: management and outcome at the Ohio State University from 1969 to 1995

To review the management strategies and outcome in gravidas with anti-M isoimmunization over the past 26 years at The Ohio State University.

Data collected from 115 pregnancies found to have anti-M antibody at The Ohio State University from September 1969 through February 1996 were reviewed retrospectively. We analyzed indirect antiglobulin tests, amniotic fluid with spectrophotometric examination, direct antiglobulin tests, M antigen status, antepartum course, and perinatal outcome.

Anti-M antibody was found in 90 women who had 115 pregnancies over 26 years. Among those with positive indirect antiglobulin tests, 104 pregnancies had titers at or below 1:4. Only one patient with an initial low titer experienced more than a three-fold increase to 1:64. Two women underwent a total of eight amniocenteses when titers were at or above 1:128. Forty-two (60%) of the 70 infants tested were positive for M antigen. Nine infants required phototherapy. Eight of these infants were delivered preterm. There was an increase in the number of women seen with anti-M antibody in pregnancy at our institution, with nearly 10% of all gravidas with a positive antibody screen having anti-M alloantibodies. There were no cases of hemolytic disease of the newborn, mild or severe.

The prevalence of anti-M isoimmunization may be increasing. The incidence of severe hemolytic disease of the newborn due to anti-M is extremely low. We found no cases in our review of 115 pregnancies, although there have been several cases of severe hemolytic disease of the newborn reported. If anti-M is detected in pregnancy, the titer is low (no more than 1:4), and there is no history of prior pregnancy complications suggesting a hemolytic disease process, we recommend no further testing other than an indirect antiglobulin test at 28 weeks to look for the emergence of other alloantibodies. However, if the initial titer is elevated or there is a concerning obstetric history, serial titers should be performed and amniocenteses reserved for rising titers.