I would say this is Herpes, and here are my reasons : 1) Pregnancy is the state which is all about protecting fetus from getting damaged by mothers immune system which could be recognized as foreign matter.Due to such comprises, certain "organisms " such as Herpes simplex virus may reactivate in more frequent, sever or/and wide spread fashion. 2) All vesicles are on the same stage of development w/o any visible scratch marks "no itching"or ruptured lesions in addition, the base of vesicles are bright red contrary to chronic dz.associated dermatitis therefore tells me that the lesions are Acute in nature.