GDF15 and major depressive disorder: Therefore, we propose a VNS-based model, which acts on multiple possible pathways for alleviating NVP/HG by (1) attenuating disruptions in gastrointestinal tract movement and function, (2) managing markers (e.g., GDF15/MIC-1) of genes and placental function, (3) regulating Helicobacter pylori, and (4) managing psychosocial factors such as anxiety and depression.