Common over the counter creams that fight cold sores, like Acyclovir or Valtrex and especially prescription drugs are best avoided in pregnancy. More natural cures for herpes, like tooth paste on the spot of the fever blister, or tea tree oil treatments, do not work as well and as fast, but are safer while you are expecting a baby. As always, there are always pros and cons, and they are best discussed with your doctor. One thing that you should be aware of if you get a secondary herpes outbreak in your third trimester is that herpes can be extremely dangerous to newborns, and can even cause death. Primary outbreaks, the first time you get herpes, are more dangerous than secondary outbreaks, but all cold sores can pose risks. Herpes can damage a newborn's brain and other organs, and can cause a very serious eye infection as well.
Therefore, if you have a herpes outbreak in the third trimester, treating it immediately is essential. Even kissing your new baby could lead to very serious long-term consequences if you happen to have a cold sore when your baby is born. If you already have a newborn, and get herpes, make sure to get in touch with a doctor immediately. They will help you treat the outbreak and advise you what to do to avoid passing the virus on to your baby.