Yes, you are right to voice your concern, but the quantity and exposure come into play again. However, avoiding either working with or exposing yourself to fertilizers and insecticides is the safer option to take. You do not want to be exposed to toxins unnecessarily, especially during your pregnancy. You may want to avoid home fumigations during this time as well. Lawn fertilizer is quickly watered down and absorbed into the soil, posing minimal risk, if any. Rather stay safe and avoid any direct contact. Wearing shoes while walking on grass prevents any absorption through the skin and exposes open cuts on your feet to the chemicals.