Being in the sun isnt very harmful to your baby. The main thing people worry about is getting dehydrated as its very easy to whilst pregnant. Its been said that you should try and avoid beaches, or if you cant, make sure you have plenty and plenty of water available, and if there is any shade areas, visit them every hour or so just to cool down a bit.
Being by the pool is fine, just make sure you keep ontop of sunblock. Especially around your stomach as the skin is thinner than normal. And also drink a glass of water for every extra hour you are out in the sun.
I dont think being in the sun brings any dangerous harm to your body, its just what it can do if you dont look after yourself. If you just follow the guidlines and take care of yourself youll be fine
EDIT : Forgot to add. Heat can also trigger nausea, in some cases quite bad. So try not to stay out longer than you need to .
xx