Fig. 2
Forest plot of the association between antibodies to pregnancy-associated P. falciparum antigens and placental malaria. a Estimates represent the odds of placental malaria in Ab responders compared with Ab non-responders, where antibodies were measured at delivery (cross-sectional studies). b Estimates represent the relative risk of placental malaria in Ab responders compared to Ab non-responders, where antibodies were measured at various times during pregnancy, as indicated (prospective studies). Estimates are for all gravidities included in original studies. Staalsoe et al. (Yaounde site) included secundigravidae and multigravidae only; Babakhanyan et al. [52] included multigravidae only; and Cox et al. [55] included primigravidae only. Estimate for McLean et al. [63] represents IgG3 responders only as total IgG was not available. Meta-analysis was only performed on estimates where VAR2CSA antigen or functional assay (where applicable) and timing of antibody determination were the same. Meta-analysis of Ab responses to FV2 and odds of PM showed a high degree of heterogeneity (I2 = 93.1%, P < 0.001) so results were not pooled. aEstimate calculated by current authors from data in original publication; bData supplied by original authors and estimate calculated by current authors. CC, case-control; CS, cross-sectional; CSA adhes. inhib., CSA adhesion inhibition assay; flow cyto., flow cytometry; n, number of participants included in estimate; OR, odds ratio; plac. isolate, placental isolate; pRBC, parasitized red blood cells; RCT, randomized controlled trial; RR, risk ratio