Having a slight fever during pregnancy usually does not cause any harm to the unborn baby.
But if your temperature of the fever you have is 100 F and doesn't go down soon then the fever during the pregnancy can be dangerous to the unborn baby.
If you have a fever of 100 F or above and can't get it to go down you need to go to urgent care or the emergency room for treatment.
If the fever is left untreated then it could harm the baby inside you so to be safe you should go get medical attention for the fever.
A slight fever that goes away soon should not be harmful for the baby during pregnancy but just in case it would be a good idea to get medical attention.
If you have a fever during pregnancy and don't have the flu then it's not normal to have the fever during pregnancy as it means something is wrong.
So when you're pregnant and you suddenly develop a fever but don't have the flu etc then seek medical attention because it's not normal.