Factors such as lack of oxygen, infection, or stress and lack of healthy foods in the mother during pregnancy, might result in a slight increase in the risk of schizophrenia later in life. People who have schizophrenia are more likely to have been born in winter or spring (at least in the northern half of the world). This might relate to increased rates of exposures to viruses before birth. This difference is about 5 to 8 percent.