Pregnant women with genital herpes are often extremely concerned about the effects, if any, of the virus on their unborn child. The main concern is that the baby may become infected with the virus during the birth and develop 'neonatal herpes'. The reality is that the transmission rate of the herpes virus from mother to baby is extremely low. This is because babies of women, who carried the herpes virus before they were pregnant, have given their baby a natural protection during the pregnancy.
The mother's antibodies (that fight against the virus) are naturally passed onto her baby through the placenta, increasing her baby's immunity. If the mother had herpes before she was pregnant and has a herpes outbreak at the birth, the chances of her baby developing 'neonatal herpes' are thought to be 0.25 to 5%. The range of occurrence can be related to if the waters have been broken for more than 4 hours before the birth. 'Prolonged rupture of membranes' when the woman is experiencing a herpes outbreak can increase the chances to around the 5% range. If the waters are not broken for a long period of time it would be more around the 0.25% range. If there are no signs of a herpes outbreak during labour, the transmission rate to the baby is about 4 in 10,000 (0.0004%).
Women, who first become infected with the herpes virus during the first 28 weeks of their pregnancy, are usually able to develop enough antibodies to protect their baby by the time they are born. The antibodies start crossing the placenta at about 28 weeks of the pregnancy, and by the time the baby is due, they often have the 'maximum' amount of immunity. Premature babies (less than 37 weeks) may not be as protected. If the baby is less than 28 weeks
gestation when born, they will not have any protection.
Mothers who contract the virus after 28 weeks of the pregnancy may not be able to produce enough antibodies in time to provide a level of protection for their baby at birth.