Management of a herpes attack depends on whether it is a first infection or recurrence, because the levels of virus in your body (the viral load) will be different with different associated risk.
1st and 2nd trimester
Confirm diagnosis. Viral isolation and typing should be carried out using ulcer swabbing, viral culture and/or PCR. Testing of paired sera, if a booking specimen is available, may help identify primary from recurrent infection.
Manage symptomatically according to patient need with Aciclovir. Refer the woman to a genito-urinary medicine clinic. Aim for a vaginal delivery.
When primary infection occurs during the 3rd trimester it carries the greatest risk of neonatal infection. The quoted risk of neonatal herpes, calculated from five studies, when the baby is delivered vaginally was 41%. A Caesarean section should be considered, especially if >34/40 gestation. (The woman can still be shedding the virus at delivery, even if there are no visible lesions.)
Management of recurrent infection
Recurrent genital herpes is associated with a much smaller risk of neonatal herpes. One study reported a transmission rate of 3% while another study reported a rate of 0%. Maternal antibodies will give some protection to the baby but neonatal infection can still occur. Regular viral swabs and culture in late pregnancy do not predict viral shedding at term and are not recommended. Aim for vaginal delivery if there are no genital lesions present at the time of labour. If there are genital lesions present at the onset of labour, current UK practice is that a Caesarean section is performed.