Maternal thyroid-gut dynamics during pregnancy and cognitive trajectories in children.

The thyroid-gut axis is a bidirectional system linking maternal endocrine function and gut microbiota, with important implications for fetal brain development. During pregnancy, maternal thyroid hormones (thyroxine and triiodothyronine) regulate neuronal growth, migration, myelination, and synapse formation. Maternal hypothyroidism, even in mild forms, can disrupt these processes, impairing neurogenesis, cortical development, and long-term cognitive outcomes in offspring. At the same time, maternal gut microbiota undergoes dynamic changes that influence thyroid hormone balance, nutrient absorption, and immune signaling through metabolites such as short-chain fatty acids, bile acids, and tryptophan derivatives. Dysbiosis may alter deiodinase activity, weaken intestinal barrier integrity, and promote inflammation, worsening thyroid dysfunction and increasing fetal vulnerability. Evidence suggests a feedback loop where microbiota affects thyroid homeostasis and thyroid hormones shape gut ecology. Emerging research indicates that microbiota-targeted therapies, diet, and environmental interventions may help restore balance, though key mechanistic gaps remain.