Fifth Disease and Pregnancy

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Many years ago, when I practiced in New England, I often didn’t have to go outside the office to know what season it was. If I was seeing an overwhelming number of colds, sore throats, and wheezing illnesses, I knew that I would have a rather icy drive home. And in the spring, I could almost smell the forsythia from the exam rooms when children came in with a certain characteristic body rash along with very red cheeks.

The rash I’m talking about here belongs to an illness known as fifth disease. Also known as erythema infectiosum, fifth disease remains a mainstay of school-age illness. However, as we shall see, discussion of the illness has its place in a pregnancy blog: it can affect all ages, and does have some implications for an unborn baby.

Fifth Disease—First Lesson

First of all, what’s up with the unusual name? Way back when, when we knew less about a lot of infectious diseases, certain childhood infections, all of which were associated with some rash or other, were assigned ordinal numbers. While the others have long since been known by different names (measles, for example, was one of them), the name “fifth disease” stuck—possibly because we didn’t know as much about what caused it. In the 1980s, however, it was found to be caused by a virus known as parvovirus B19.

The virus characteristically affects school-age children, most commonly during the late winter and early spring. Keep in mind, however, that the virus doesn’t always read the textbook, and can infect all ages during all seasons. Since it can be transmitted through saliva or sputum, it moves fairly easily from person to person.

Like so many viruses, early symptoms of fifth disease are pretty nonspecific: a little fever, cough, headache, sore throat. (From about adolescence onward, people who get the disease are a little more under the weather, with symptoms often including joint pain.) About 7 to 10 days after these symptoms, however, there is usually a characteristic rash that helps physicians nail the diagnosis. It starts with very red cheeks (known by the very scientific term “slapped cheek appearance”) and is followed by a rash on the body, which starts as small bumps and then can have a lacy appearance. Not every rash is typical, however, which is why someone can have fifth disease without knowing it.

Although the rash can come and go for a few weeks, that’s about it for most people, and the disease passes without too much hassle. However, we get concerned about it in three populations: (1) people with certain types of hereditary anemias such as sickle-cell disease, (2) people with immune deficiencies, and (3) our concern here: pregnant women.

Pregnant Women and Fifth Disease

If a pregnant woman gets fifth disease, there’s a chance it can affect her unborn child. The fetus can suffer a severe anemia. One consequence of this is fetal heart failure, leading to a condition called hydrops fetalis. Miscarriage or death of the fetus can result. (Some hydrops is treatable through fetal blood transfusion, but the treatment is difficult to say the least, and definitely not a slam-dunk.)

The chance of the complication in a woman who contracts the virus is about 5%. However, about 50% of women have had fifth disease, whether or not they know it—meaning, for all intents and purposes, assuming everyone exposed could get infected, the chance of a fetal complication if Mom-to-be doesn’t know her infection status is 2.5%. To put this in perspective, keep in mind that the rate of miscarriage from all causes is thought to be at least 10%.

There’s Fifth Disease in the School! Now What?

One of the good news/bad news things about fifth disease is that people with the characteristic rash are no longer contagious. However, they can definitely pass on the virus in the days before the rash appears. Thus, if it’s going around, the chance of a pregnant woman being exposed is increased. There’s no vaccine for the disease, and while there are blood tests—both to see if someone is infected at the moment, and to see if someone was infected in the past (and thus immune now)—like many tests for viruses, their use is limited in many situations due to the tests’ turnaround time. (We used to joke that the baby would be in college by the time the test came back. It might be a little better than that now, but testing is still unlikely to be helpful in most acute situations.)

What, then, is a pregnant woman to do when it’s fifth disease time? There’s no one answer to this. Coming up with the one that’s best for you and your baby requires a conversation with your obstetrician, your family, your employer, your children’s school, and any other stakeholders that involve potential exposure. While most sources recommend not much restriction of activities, it’s important to know about the illness, its small but increased risk to the fetus, and the importance of keeping your obstetrician in the loop should you become exposed. Your provider will follow the pregnancy more closely, usually with multiple ultrasounds. One thing that’s always prudent to do, however, is help control the spread of all infections by good handwashing, good cough/sneeze hygiene, and avoiding obviously ill contacts.

Stan Sack
Dr. Stan Sack has 29 years’ experience as a primary care pediatrician in Massachusetts and Florida. A medical writer since 2015, he enjoys blogging on topics that are on parents’ minds but are covered less often in books and on websites. He lives in the Florida Keys with his family and enjoys healthy cooking, fitness activities and singing in his spare time.

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