What are the risks of parvovirus to my fetus?

Q: I am 12 weeks pregnant and have tested positive for exposure to parvovirus B19. What are the risks of this affecting the fetus? Is there specific testing besides ultrasound that can be done to make sure the fetus has not been infected?

A: There is cause for concern, but no need to panic.

Although we don?t have much in the way of statistics on the risks of transmission and harm to the fetus, the risk of losing your baby is believed to be small. The U.S. government estimates the risk of pregnancy loss from parvovirus to be less than 5 percent. Other estimates place this risk slightly higher, up to 10 percent.

We think that a pregnant woman?s chances of transmitting the virus to the baby are no greater than 1 in 3. And even when the fetus is infected, it doesn?t usually lead to problems.

When there are problems, parvovirus B19 can cause a severe kind of anemia that may lead to miscarriage or stillbirth. There?s also a slight chance of inflammation of the heart. There is no evidence of birth defects from parvovirus B19 infection.

Has it been confirmed that you actually had fifth disease while pregnant? The blood test indicates exposure to the virus within the past few months. That would make it possible for you to have had the disease before you became pregnant.

Doctors are not in complete agreement about the best course of action when infection is suspected. Besides monitoring the fetus with ultrasound, doctors may order blood tests. But the value of the tests and even the ultrasound has yet to be proven.

I suggest that you have an in-depth discussion with your obstetrician about the situation and your options. Beyond that, you can be comforted that the odds are strongly in your favor. And as the weeks wear on, the chances of any problems from parvovirus infection will drop.

By the way, this is a different parvovirus from the one that infects dogs. Humans and dogs cannot transmit the virus across species.