Abstract: Objective This study retrospectively investigates and analyzes the occurrence of ABO hemolytic disease of the fetus and newborn (ABO-HDFN) at Nanjing Maternal and Child Health Hospital. It aims to explore the factors influencing bilirubin levels and serological test results in children diagnosed with ABO-HDFN. Methods A total of 1 131 children diagnosed with ABO-HDFN between January 2022 and December 2023 were selected for analysis. Serum total bilirubin (TBIL), indirect bilirubin (IBIL), hemoglobin (Hb), and carboxyhemoglobin (COHb) levels were measured. Additionally, three serological tests for hemolysis were performed. Clinical data, including birth weight, gestational age, and neonatal age, were collected to analyze the factors influencing bilirubin levels, the incidence of hemolysis, and its severity. Results Among the 1 131 children diagnosed with ABO hemolysis, the median gestational age was 39.14 (38, 40.14) weeks, and the median birth weight was 3 240 (2 890, 3 540) grams. Significant differences in TBIL and IBIL levels were observed in relation to birth weight, multiple births, gestational age, mode of delivery, feeding method, and neonatal age (P<0.05). However, there were no significant differences in TBIL and IBIL levels based on gender, blood type, or gravida (P>0.05). The direct antiglobulin test (DAT) had a positive rate of 19.36% (219/1 131), the free antibody test had a positive rate of 84.08% (951/1 131), and the release test had a positive rate of 100%. Based on the serological test results, the children were categorized into "three positives," "two positives," and "one positive" groups, with significant differences in TBIL, IBIL, Hb, and COHb levels among these groups (P<0.05). The highest positive rates for DAT and the free antibody test were observed in children aged≤3 days, at 29.22% (161/551) and 90.74% (500/551), respectively. In children aged 4-7 days, the positive rates were 11.31% (57/504) and 79.96% (403/504), respectively, while in children aged ≥8 days, the rates were 1.32% (1/76) and 63.1% (48/76), respectively. As neonatal age increased, the positive rates for DAT and the free antibody test significantly decreased (P<0.001). Conclusion The severity of ABO-HDFN is associated with the results of the three serological tests, as well as Hb and COHb levels. For children with maternal-infant ABO blood type incompatibility, timely monitoring of bilirubin levels and performing the three serological tests are crucial for the prevention and management of ABO-HDFN.

Key words: Bilirubin levels, ABO-Hemolytic disease of the fetus and newborn, Serological test, Neonatal age