Hi Bevth, 3.9 is quite low so you have a couple of options really depending on your current regime. Do you take set amounts of insulin ? Or do you carb count and adjust as required ? If you take set amounts, you could have an additional snack such as a slice of bread with your meal. If you count carbs, just take adjust accordingly depending on your ration. I would, for instance, take 1 unit less than normal. Also, test before bed to make sure you're within target range. Good luck !
Mo