Infection during pregnancy
the risk of aquiring parvovirus during pregnancy, averaged over epidemic and non-epidemic years, is about 1/400. The risk of infection for a non-immune mother with a child who has fifth disease is between 50 and 90%, whereas for a child say in a day care with another who is infected, is lower at about 20-30%.
Parvovirus is a danger to the unborn child in two ways. Firstly there is an increased risk of miscarriage if the infection is aquired during the first 20 weeks of pregnancy. The overall risk of miscarriage following parvovirus infection is around 15%, the infection representing an increase of 9%, and being most marked between 9 and 16 weeks gestation.
The other problem parvovirus can cause is an anaemia, or low blood count, in the baby. This leads to a condition known as hydrops fetalis, where the baby, amongst other things, carries a lot of excess water. A fetus is most likely to develop hydrops when a mother has a parvovirus infection between 9 and 20 weeks gestation. Even if it is acquired at this time, there is overall only a 3% chance of hydrops developing. Hydrops doesn't usually develop immediately. A pregnant woman who has confirmed parvovirus infection would be offered scans, which can detect if the baby is becoming anaemic. The interval between infection with parvovirus and development of hydrops varies between 2 and 17 weeks. It seems likely that an early blood transfusion will improve the chances for an affected baby's survival.
Thus, a woman who is pregnant, not knowing her immune status and who is exposed to parvovirus infection between 9-20 weeks has a 0.6% risk of hydrops developing and a 4% increase in risk of miscarriage.
Close contact placing a woman at risk of catching parvovirus includes the following:
* living in a houshold setting with an infected person
* sharing a meal with an infected person
* or being in the same room for over half an hour as an infected person
follow-up of infants who were exposed to parvovirus in the womb has now been reported up to the age of 10 years. It seems that there are no long-term effects from an infection which doesn't cause miscarriage or hydrops (as most do not).
Once a woman has had parvovirus infection, she is not at risk of getting it again, whether it was acquired during pregnancy or not. It is not a cause of recurring miscarriage.