In terms of an unborn child's health, I believe there's a difference between primary and secondary HSV.
Primary HSV is when you contract HSV for the first time and get a lesion in the vaginal area. This is most dangerous for baby and even more so if you have a vaginal delivery. The danger is reduced with antivirals (aciclovir or ganciclovir) if given in time but the danger remains at a level that most first world countries would consider a high risk pregnancy.
Secondary HSV is when you have already contracted HSV, had your primary lesion a while back and then break out in the future with your second, third, fourth or fifth etc lesion. Any lesions after the primary outbreak are called "secondary" outbreaks. These are much less dangerous to the unborn child because the HSV viral load is less. I am uncertain of the specifics, but depending on the wealth of your country or the literature you read, it may or may not be cost-beneficial (from the point of view of the baby's health) to be treated with antivirals for secondary outbreaks.
In summary, if you've never had HSV 1 or 2 before, then contracting it whilst pregnant is dangerous for the unborn child. HSV 2 tends to manifest in the vaginal region and primarily for that reason is thought to be the more dangerous of the two from an unborn child's perspective. If you already have had primary HSV1 or 2 and the illness has run its course into remission, then the danger to potential future babies of yours is low, but may still require treatment depending on the guidelines your country follows.
There is the additional concern of HSV lesions popping up on parents while the child is still young (age less than 1 year, and even more so, age less than 3 months) but that is a separate topic of discussion I think.
