Clinical impact and prevalence of IgG1 and IgG3 subclasses in antenatal alloimmunized women: experience from a tertiary medical centre in South India

Background Haemolytic disease of the foetus and newborn (HDFN) occurs due to maternal sensitization to paternal antigens. According to literature, IgG1 and IgG3 have a greater impact when compared to IgG2 and IgG4. To date, there is limited literature available from India. The current study was therefore executed using the column agglutination technique (CAT) for subclass identification (IgG1 and IgG3). The findings might be important to facilitate early referral, to centers where appropriate care is possible. Methodology Eighty‐five alloimmunized antenatal women were included in the study. IgG subclass (IgG1/IgG3) was determined using the ‘DAT IgG1/IgG3 ID’ card (Bio‐Rad). Pregnancies were followed up and categorized into ‘no/mild/moderate’ or ‘severe’ HDFN. Prevalence was calculated and severity of HDFN was correlated with subclass. Result In alloimmunized women (2·18%), the prevalence of IgG subclass was 20% for IgG1, 3·53% for IgG3, 24·71% for IgG1 + IgG3 and 51·76% had neither IgG1 nor IgG3. There was a highly significant difference between disease severity and the absence/presence of IgG1/IgG3 – either singly or in combination (P < 0·001) in newborns at risk. The risk of severe HDFN increased a sevenfold: it was lowest in patients with neither IgG1 nor IgG3, when compared to having either one of them or both (P < 0·05, CI between 1·5–31·89). Conclusion The presence of IgG1/IgG3 subclass has a significant impact on the severity of HDFN. Therefore, these mothers require close antenatal monitoring to provide appropriate and timely intervention for newborns. CAT is a feasible option to identify high‐risk pregnancies and facilitate early referral.