Acoustic markers of emotional expression in professional lyrical singing.

Perinatal depression (PND) affects approximately 10%–20% of mothers worldwide and has been linked to a range of adverse outcomes for both mothers and offspring, including preterm birth, altered neurodevelopment, and longer-term emotional and cognitive difficulties (, , , ). Beyond its psychiatric manifestations, pregnancy and the postpartum period represent a biologically dynamic phase characterized by substantial endocrine, metabolic, and immune adaptation required to support maternal and fetal homeostasis (, ). Increasing evidence suggests that PND is accompanied by deviations from typical perinatal physiological trajectories across multiple biological systems, rather than reflecting dysfunction within a single pathway (). Nevertheless, clinical identification of PND continues to rely largely on self-report instruments, underscoring the limited integration of biological information into current assessment frameworks and motivating interest in system-level biological characterization (, ). Bidirectional interactions between the microbiota and the central nervous system are closely intertwined with host immune and metabolic regulation (, ). While the majority of existing work has focused on the gut microbiome, the oral cavity constitutes a distinct and immunologically active microbial ecosystem that interfaces directly with host barrier tissues and systemic circulation (, ). Recent studies have reported associations between oral microbial features and depressive or anxiety-related symptoms, with functional signals implicating pathways related to lipopolysaccharide biosynthesis, virulence-associated functional categories, and microbial energy metabolism (). Importantly, such functional differences have been observed in the absence of pronounced shifts in overall microbial community structure, suggesting that functional profiling may capture biologically relevant variation not reflected by taxonomic composition alone. This distinction may be particularly relevant during the perinatal period, when endocrine and immune transitions are pronounced, and host sensitivity to microbial-derived signals may be altered (, ). At the systemic level, perinatal metabolic regulation undergoes marked reorganization. Steroid-related metabolites, bile acids, and lipid mediators play central roles in coordinating immune modulation and metabolic homeostasis, and variation in these pathways has been implicated in mood disorders and stress-related conditions (, ). However, oral microbial functional characteristics and circulating metabolic features are rarely examined jointly within the same individuals, limiting insight into how compartment-specific biological variation may relate across biological systems in the context of PND.