Influenza infection during which trimester is mentioned as potentially affecting fetal development and possibly influencing schizophrenia risk?

• A. Second trimester
• B. First trimester
• C. Third trimester
• D. At birth

Answer: (A)

Exposure to influenza at a specific time during pregnancy can shape how the fetal brain develops, because different stages of brain growth happen at different times. The second trimester is a particularly important window because it involves rapid brain wiring—neuron connections are forming and refining circuits. When the mother has influenza, her immune system responds and releases inflammatory signals that can reach the developing fetus. These signals can influence how neural cells migrate, differentiate, and form synapses, potentially leading to lasting changes in brain connectivity. Such developmental perturbations are thought to contribute, in part, to the risk of schizophrenia later in life. Exposures in the first trimester tend to affect organ formation more broadly, while born-at-birth or late-pregnancy exposures affect other aspects of development, making the second trimester a window notably associated with schizophrenia risk in this context.