Background Blood group O protects African children against severe malaria and
has reached high prevalence in malarious regions. However, its role in malaria
in pregnancy is ambiguous. In 839 delivering Ghanaian women, associations of
ABO blood groups with Plasmodium falciparum infection were examined. Methods
Plasmodium falciparum infection was diagnosed in placental blood samples by
microscopy and PCR assays. Present or past infection was defined as the
detection of parasitaemia or haemozoin by microscopy, or a positive PCR
result. Blood groups were inferred from genotyping rs8176719 (indicating the O
allele) and rs8176746/rs8176747 (distinguishing the B allele from the A
allele). Results The majority of women had blood group O (55.4%); present or
past P. falciparum infection was seen in 62.3% of all women. Among multiparae,
the blood groups had no influence on P. falciparum infection. In contrast,
primiparae with blood group O had significantly less present or past infection
than women with non-O blood groups (61.5 vs 76.2%, P = 0.007). In multivariate
analysis, the odds of present or past placental P. falciparum infection were
reduced by 45% in blood group O primiparae (aOR, 0.55 [95% CI, 0.33–0.94]).
Conclusions The present study shows a clear protective effect of blood group O
against malaria in primiparae. This accords with findings in severe malaria
and in vitro results. The data underline the relevance of host genetic
protection among primiparae, i.e. the high-risk group for malaria in
pregnancy, and contribute to the understanding of high O allele frequencies in
Africa