Any fever in pregnancy has to be taken seriously as it has serious implications of the health of the mother as well as the baby.
The cause of fever should be investigated, hence I recommend that you visit a Gynaecologist first who shall refer you further if needed:
Please mention to your physician
Duration of fever with recording of temperature and time.
Presence of rash
Presence of urinary or stool difficulty.
Breathing difficulty, cough or chest pain.
Presence of communicable illnesses like dengue, malaria, TB, H1N1 in your family and community, hepatitis.
Also mention all the vaccination recieved by her till date.