Fig. 3.

Examples of causal diagrams of multi-omic research questions using mediation analysis. a represents a single metabolomic pathway as a mediator on the causal pathway between air pollution and adverse birth outcomes. b represents multiple ordered metabolomic pathways as mediators on the causal pathway between air pollution and adverse birth outcomes. c represents multiple metabolomic pathways treated as an unordered set of mediators on the causal pathway between air pollution and adverse birth outcomes