Maternal immunoglobulin G anti-A and anti-B antibody titres for predicting neonatal immune sensitisation in ABO-incompatible pregnancies: The Maternal Anti-A and Anti-B Antibody Titres in ABO-Incompatible Pregnancies study.

BACKGROUND AND

OBJECTIVES

Maternal immunoglobulin G (IgG) anti-A and anti-B antibodies can cross the placenta and cause ABO haemolytic disease of the foetus and newborn (ABO-HDFN). We aimed to evaluate whether maternal IgG anti-A and anti-B titres predict neonatal direct antiglobulin test (DAT) positivity in ABO-incompatible pregnancies.

MATERIALS AND

METHODS

In this prospective observational cohort study, 889 consecutive ABO-incompatible mother-newborn pairs were enrolled between November 2025 and June 2026. Maternal IgG anti-A and anti-B titres were measured after 0.01 M dithiothreitol treatment using the conventional tube antiglobulin titration method. Neonatal ABO grouping and DAT were performed by column agglutination technology. Receiver operating characteristic (ROC) curve analysis and multivariable logistic regression assessed the predictive performance of maternal antibody titres.

RESULTS

Overall, 112/889 (12.6%) neonates were DAT positive. Maternal IgG anti-A and anti-B titres were significantly higher in mothers of DAT-positive neonates (both p < 0.001). Maternal IgG anti-A (area under the curve [AUC] 0.778) and anti-B (AUC 0.803) showed acceptable diagnostic performance. Higher thresholds (anti-A ≥32; anti-B ≥16) achieved 100% specificity, whereas lower thresholds (anti-A ≥8; anti-B ≥4) provided high sensitivity for excluding neonatal DAT positivity. Increasing maternal IgG anti-A (adjusted odds ratio [aOR] 1.12, 95% confidence interval [CI]: 1.06-1.18) and anti-B titres (aOR 1.18, 95% CI: 1.09-1.28) independently predicted DAT positivity (both p < 0.001). Most DAT-positive neonates required phototherapy (94.6%) but none required exchange transfusion.

CONCLUSION

Standardised maternal IgG anti-A and anti-B titres independently could predict neonatal DAT positivity. A dual-threshold approach may complement existing antenatal assessment by identifying high-risk pregnancies and guiding individualised postnatal surveillance.