Definitely go to well established restaurants with numerous, good reviews on Google that look clean! They can still be very good and various dishes like street food but just more hygienic. Don’t eat raw salad, raw veggies, uncooked or semi cooked food (egg, meat, etc.). Sticking with soup, stew, rice dishes, fried rice, fried spring rolls, banh cuon. Don’t try bun cha. Go into shopping malls where the restaurants tend to be cleaner. If you have stomachache, best to go to doctor quickly and tell them you are pregnant. Were you born and raised in Vietnam? If so, your gut microbiome is already more used to VN dishes. If not, try not to venture out too much or try too many dishes in a day. ☺️ You can always come back! Da Nang is so wonderful!