Parvovirus
What is parvovirus?
Parvovirus B19 (also known as slapped cheek syndrome, fifth disease) is a virus that commonly infects children. It is usually transmitted by coughing and sneezing (respiratory droplets). Hand washing is important in helping to prevent spread. School teachers, childcare workers and mothers of young children are particularly likely to be exposed to this virus as it is commonest amongst younger school age children, but everyone can be exposed to it. It is such a common childhood illness that 60-75% of pregnant women are immune.
For most healthy people, Parvovirus B19 causes a mild, self-limiting illness which is followed by life-long immunity. It often runs in epidemics through schools in late winter, causing a high fever, a facial rash. After exposure, a woman may remain infectious for the following 3-10 days or until the rash appears.
What are the risks if parvovirus infects my baby in the womb?
When a mother contracts parvovirus B19, the risk of passing the infection to her baby (‘vertical transmission’) is around a third or 33%. The virus attaches to precursors to red blood cells which carry oxygen and haemoglobin in blood. The virus prevents new red blood cells from being formed resulting in anaemia which in a few cases may result in heart failure, hydrops and fetal death if untreated.
The virus does not cause any fetal anomaly as such, but it can infect the fetal bone marrow, heart muscle and liver. If the fetus is infected and does cause anaemia, it may either resolve spontaneously, or cause severe anaemia with hydrops (swelling in at least 2 areas of the fetus) in up to 13% of cases. If hydrops occurs the risk of fetal death if untreated is 50% and 95% of these fetuses will have low platelets (thrombocytopaenia).
When maternal parvovirus infection is confirmed via blood tests, the mother will be referred to a fetal medicine specialist 4 weeks after exposure for regular scans every 1-2 weeks for the subsequent 12 weeks to monitor for signs of developing anaemia. The fetal medicine doctor measures the speed of blood flowing through the fetal brain to work out whether there is anaemia. If anaemia is detected the fetal medicine doctor may offer for the baby to receive a blood transfusion while the baby is still in the womb, to correct the anaemia. Because this is an invasive procedure, they will discuss the risks and benefits with you, as we know that the hydrops will resolve spontaneously in a third of cases, but following intrauterine transfusion, the hydrops will resolve in 55% of cases.
If I opt for fetal blood transfusion, what is the outcome for my baby?
Studies show that after fetal blood transfusion 85% of babies will survive. If transfusion was not given, 55% of babies will survive. In terms of long term neurological brain function, evidence suggests around 10% of children will have neurodevelopmental delay. The consensus is that the severe anaemia and hydrops may cause the brain disability rather than the parvovirus itself. The fetal medicine doctor may discuss the option of brain MRI with you after your baby has recovered from the anaemia.