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Reassessing critical maternal antibody threshold in RhD alloimmunization: a 16‐year retrospective cohort study
Author(s) -
Walsh C. A.,
Doyle B.,
Quigley J.,
McAuliffe F. M.,
Fitzgerald J.,
Mahony R.,
Higgins S.,
Carroll S.,
McParland P.
Publication year - 2014
Publication title -
ultrasound in obstetrics and gynecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.202
H-Index - 141
eISSN - 1469-0705
pISSN - 0960-7692
DOI - 10.1002/uog.13383
Subject(s) - medicine , retrospective cohort study , obstetrics , anemia , pregnancy , cohort , fetus , referral , antibody , population , cohort study , hemoglobin , fetal hemoglobin , pediatrics , immunology , biology , genetics , environmental health , family medicine
ABSTRACT Objective To determine the critical maternal antibody threshold for specialist referral in cases of RhD alloimmunization. Methods This was a retrospective cohort study, covering a 16‐year period at the national tertiary fetal medicine center for management of alloimmunization. Data concerning RhD alloimmunized pregnant women were extracted from an institutional database and maternal anti‐D antibody levels were cross‐checked with the national reference laboratory. Fetal hemoglobin (Hb) levels were determined only at the first intrauterine transfusion ( IUT ) and were compared with the pretransfusion maternal anti‐D antibody level ( IU / mL ). Sensitivity, specificity and positive and negative predictive values of maternal antibody thresholds for detecting moderate to severe (Hb ≤ 0. 64MoM ) fetal anemia were calculated. Results Between 1996 and 2011, 66 women underwent a first IUT for RhD alloimmunization at our institution. The highest serum anti‐D antibody level was extracted for 208 RhD alloimmunized women who did not require IUT during the last 10 years of the study period. The traditional maternal antibody threshold of > 15 IU / mL failed to detect 20% of cases of moderate to severe fetal anemia. The ≥ 4 IU / mL threshold had 100% sensitivity but a 45% false‐positive rate. The optimal anti‐D antibody threshold for specialist referral in our population was ≥ 6 IU / mL ; at this level, no case of moderate to severe anemia was missed and specificity was 61%. Use of this threshold would have eliminated 10% of referrals to our fetal medicine unit without compromising fetal outcomes. Conclusions Setting the critical maternal RhD antibody level at >15 IU / mL does not provide sufficient sensitivity. The lower threshold of ≥ 4 IU / mL , though sensitive, is associated with a 45% false‐positive rate. In our population, a threshold of ≥ 6 IU / mL minimizes false‐positive referrals while maintaining 100% sensitivity for moderate to severe fetal anemia. Copyright © 2014 ISUOG. Published by John Wiley & Sons Ltd.