Herpes antibodies in the mother's blood cross the placenta to the fetus.
These antibodies help protect the baby from acquiring infection during birth, even if there is some virus in the birth canal.
In addition, newly infected people - whether pregnant or not - have a higher rate of asymptomatic shedding for roughly a year following a primary episode.
This higher rate of asymptomatic shedding, plus the lack of antibodies, create the greater risk for babies whose mothers are infected in the last trimester.
However, most researchers estimate between 1,000 and 3,000 cases a year in the United States, out of a total of 4 million births.
To put this in greater perspective, an estimated 20-25% of pregnant women have genital herpes, while less than 0.1% of babies contract an infection.
About 5% of cases of neonatal herpes are contracted this way.
But please think positive thoughts and trust your doctor. While neonatal herpes is rare, women who know they have genital herpes are often concerned about the possibility of transmitting the virus to their babies at birth.
My daughter, now 12 months, is healthy and beautiful. On the one hand, such concern is understandable, because herpes can have devastating consequences for a newborn.
Babies born prematurely may be at a slightly increased risk, however, even if the mother has a long-standing infection.
This is because the transfer of maternal antibodies to the fetus begins at about 28 weeks of pregnancy and continues until birth."Babies delivered at term should be protected by antibodies -- but premature babies haven't gotten a full load, "explains Brown.