Etiological stratification and clinical implications of indirect combs test positivity in Rh-incompatible pregnancies: A retrospective cohort analysis from a tertiary care center

The Indirect Coombs (IDC) is a screening test used to detect maternal sensitization in pregnancies with Rh incompatibility.This study aims to investigate the prevalence and underlying causes of IDC test positivity in our clinic, as well as to evaluate its associated prenatal and postnatal outcomes.The study was conducted at Health Sciences University, Istanbul Training and Research Hospital, Department of Obstetrics and Gynecology, between August 2016 and 2019.The records of Rh D-negative pregnant women aged 18-40, who underwent Indirect Coombs testing for Rh incompatibility screening, were retrospectively reviewed in the system.Pregnancies with positive IDC test results were included in the study and categorized into three main groups.Group I consisted of cases with Non-Anti-D-mediated IDC positivity.Group II included cases with IDC positivity induced by Anti-D immunoglobulin prophylaxis.Group III consisted of patients with Anti-D-mediated IDC positivity without a history of immunoglobulin prophylaxis.The prenatal and postnatal outcomes of these groups were evaluated and compared.A total of 185 positive IDC test results were identified.Group I, Group II, and Group III comprised 63 (34%), 95 (51.4%), and 27 (14.6%)patients, respectively.In both Group I and Group II, even in patients with high IDC test titers, no cases of prenatal or postnatal fetal anemia were observed.In contrast, Group III demonstrated significantly higher rates of the following parameters compared to Groups I and II: evidence of fetal impact on ultrasound examination, fetal hydrops, anemia in the newborn, neonatal ICU admission, need for exchange transfusion and IVIG therapy, jaundice, phototherapy requirement, and newborn Direct Coombs positivity (z-test, p < 0.05).No significant differences were found between Groups I and II regarding these parameters, and fetal outcomes were similar in these groups.In our study, most of the positive results were due to non-Anti-D-mediated causes and previous Anti-D immunoglobulin prophylaxis applications, with similar prenatal and postnatal prognoses in these two groups.However, fetal and neonatal morbidity and mortality rates were significantly higher in Group III: the "affected Rh-D disease" group.