There is usually no fever in the early stages of pregnancy, but if some people have a high basal body temperature, which is the usual temperature of 37°C, it will rise by 0.3-0.5°C after ovulation. The temperature will persist when you are pregnant, but will not exceed 37.5°C at the highest. If it exceeds 37.5°C, it is a fever, possibly a cold, or a bacterial infection elsewhere, and must be treated as soon as possible in the hospital. Fever in early pregnancy can have an effect on pregnancy, and may cause preeclampsia, or the embryo stops developing, and must be treated as soon as possible to avoid further progression of the condition.