title: ABO blood group and the risk of placental malaria in sub-Saharan Africa.
abstract: BACKGROUND
  In malarious areas of the world, a higher proportion of the population has blood group O than in non-malarious areas. This is probably due to a survival advantage conferred either by an attenuating effect on the course of or reduction in the risk of infection by plasmodial parasites. Here, the association between ABO blood group and incidence of placental malaria was assessed in order to determine the possible influence of the former on the latter.
  
  
  METHODS
  Data from a study in Lambaréné, Gabon, and data from three previously published reports of studies in The Gambia, Malawi and Sudan, were compiled and compared. ABO blood groups were cross-tabulated with placental malaria stratified by parity. Odds ratios (OR), stratified by parity, were calculated for the outcome, placental parasitaemia, and compared between blood group O vs. non-O mothers in all four studies. Random effects meta-analysis of data from individual studies from areas with perennial hyper/holoendemic transmission was performed.
  
  
  RESULTS
  In Gabon, the odds ratio (OR) for active placental parasitaemia in mothers with group O was 0.3 (95% CI 0.05-1.8) for primiparae and 0.7 (95% CI 0.3-1.8) for multiparae. The OR for primiparae in the published study from The Gambia was 3.0 (95% CI 1.2-7.3) and, in Malawi, 2.2 (95% CI 1.1-4.3). In the Sudanese study, no OR for primiparae could be calculated. The OR for placental parasitaemia in group O multiparae was 0.8 (95% CI 0.3-1.7) in the Gambia, 0.6 (95% CI 0.4-1.0) in Malawi and 0.4 (95% CI 0.1-1.8) in Sudan. Combining data from the three studies conducted in hyper-/holo-endemic settings (Gambia, Malawi, Gabon) the OR for placental malaria in blood group O multiparae was 0.65 (95% CI 0.44-0.96) and for primiparae 1.70 (95% CI 0.67-4.33).
  
  
  CONCLUSIONS
  Studies conducted in The Gambia and Malawi suggest that blood group O confers a higher risk of active placental infection in primiparae, but a significantly lower risk in multiparae. These findings were not confirmed by the study from Gabon, in which statistically non-significant trends for reduced risk of placental parasitaemia in those with blood group O, regardless of parity, were observed.
authors.affiliation: Medical Research Unit, Albert Schweitzer Hospital, Lambaréné, Gabon.
authors.forename: Ayola A
authors.initials: AA
authors.lastname: Adegnika
authors.forename: Adrian J F
authors.initials: AJ
authors.lastname: Luty
authors.forename: Martin P
authors.initials: MP
authors.lastname: Grobusch
authors.forename: Michael
authors.initials: M
authors.lastname: Ramharter
authors.forename: Maria
authors.initials: M
authors.lastname: Yazdanbakhsh
authors.forename: Peter G
authors.initials: PG
authors.lastname: Kremsner
authors.forename: Norbert G
authors.initials: NG
authors.lastname: Schwarz
mesh_terms: D000017:ABO Blood-Group System; D000328:Adult; D017954:Africa South of the Sahara / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D008288:Malaria / Q000453:epidemiology*; D015233:Models, Statistical; D010920:Placenta / Q000469:parasitology / Q000473:pathology; D010922:Placenta Diseases / Q000453:epidemiology*; D011247:Pregnancy; D018570:Risk Assessment
chemical_list: D000017:ABO Blood-Group System