ABO-haemolytic disease of the newborn (ABO-HDN): factors influencing its severity and incidence in Venezuela.

The objective of this study was to determine the incidence of the Haemolytic Disease of the Newborn due to ABO blood group incompatibility (ABO-HDN) in the population of Caracas attending the Maternity Hospital 'Concepción Palacios'. The relationship between A and B antigens density of cord blood erythrocytes and the cytotoxic activity of antibodies in mothers' sera with the severity of the haemolytic disease, was also studied. From a sample of 245 blood group 'O' mothers, 68 gave birth to full term 'A' or 'B' blood group infants. The evolution of serum bilirubin and the routine haematological values, were followed in all the babies during 72 h after birth, allowing the diagnosis of ABO-HDN in 21 infants. Taking into account that in Venezuela the frequency of blood group 'O' is 59 per cent, it was concluded that in the general population of newborns, 16 per cent present foeto-maternal ABO incompatibility, and the incidence of ABO-HDN was near to 5 per cent. The density of the 'A' and 'B' antigens in cord red cells was studied using an immunoenzymatic assay. No statistically significant association between antigen maturity and severity of the ABO-HDN could be shown. A positive association was found between cytotoxic capacity of mothers' sera and development of ABO-HDN (P < 0.05). Twenty ABO incompatibles children presented moderate late anaemia at 3 weeks of age.