Chicken salad can safely remain in the lunch rotation during your pregnancy.
Because it’s mainly composed of cooked chicken, mayonnaise, veggies, and seasonings, there isn’t really much that can go wrong here. The main thing to be sure of is that the mayonnaise you’re using is pasteurized. Sost store-bought mayo will be—just double check the packaging. For those who are ambitious in the kitchen, it’s probably best to avoid your homemade mayonnaise, as raw eggs that have not been pasteurized are a food safety concern.
If you’re open to playing around with it, plain yogurt and avocado can be substituted for mayonnaise as well, which can be a nice way to change things up from time to time.