I just had a bad infection a couple of weeks ago and had a forty degree temp for nearly 36 hours. My bubs heart rate was up high but that is because mine was too. According to my midwife and the midwives at the hospital they actually cope really well when we are sick. I am sure there have been heaps of women who have gotten the flu etc when pregnant and I would think it would have to be an extreme temp for a long time to cause damage.