Lower maternal TNF-α has been associated with a higher mean glycemic index during third trimester, implicating a potential role for metabolic pathways during pregnancy.51 Reduced maternal TNF-α levels could also result from dysregulation of the parasympathetic nervous system following an immune response, as abnormal patterns of autonomic arousal are implicated in sex-dependent risk for depression.17 Further, nicotinic cholinergic signals transmitted by the vagus nerve to the central nervous system after bacterial endotoxin exposure can inhibit TNF-α expression.52 This evidence concerns the gene TNF and major depressive disorder.