Nausea and vomiting at the 40th day of pregnancy are mainly due to the fact that the estrogen in the body will change greatly after pregnancy and will increase a thousand times, so there will be water and sodium retention in the body, which will also lead to edema of the mucous membrane of the gastrointestinal tract. If you are dehydrated, you should go to the hospital for rehydration and correction of electrolyte disturbance. In addition, if the vomiting is not serious, it is recommended to eat something as much as possible to avoid aggravating the nausea and vomiting due to the friction of the gastric mucosa in the fasting state, and it is recommended to eat some easily digestible food.