I think I’m asked this question by patients more than any other about the cause of their subfertility. Stress can certainly prevent ovulation and lead to a lack of periods. I used to be contacted by at least one female medical student each year at the time of final exams who was panicking because she thought she was pregnant as her periods had stopped! None of them ever was. Whether stress can have an effect when the periods stay regular is unproven, but it seems a reasonable possibility.