I would start adding fruit and veggies into their diets. The pregnancy might be taking too much out of mama. After I know intercourse has occurred I start feeding the future mama cooked eggs, tuna, bigger nuts ( think Christmas nuts ), cooked pasta, and fruits/veggies. I don't do it everyday, but at least 3 days a week. Keep feeding them what you feed them now as well ( 1 bowl extras, 1 bowl regular food ). It's easy to do if you make yourself some food, make her some food too. Because of this I have exceptionally healthy rats. Beautiful coats, bright eyes, BIG litters, and I have not lost 1 baby or mama.
As for temp, I keep it at 74. Comfortable for both mom and babies!