My wife is almost five months pregnant, and she came in contact with a child infected by fifth disease. She was only in contact with the child for a few seconds, but still the thought of her being infected has us both scared. What is the chance she could be infected? If she is infected is there anything we can do to protect the baby?

Kevin

Fifth disease is an infection caused by parvovirus B19. It is characterized by fever and aches, followed by a rash that causes a "slapped-cheeks" appearance on the face and "lace-like" redness on the rest of the body. The rash is a less common symptom in adults than in children. The infection also causes joint symptoms, including arthritis of the fingers and wrists, which are especially common in women.

Parvovirus is not as contagious as some viruses. It infects about half of susceptible people after exposure. (By comparison, measles will infect more than 90 percent.) Pregnant women are at no higher risk of acquiring the infection than anyone else. After being infected, people become immune to reinfection. Almost half of all pregnant women have been infected in the past and are thus immune.

In pregnant women who do become infected, there is risk to the fetus. The risk of spontaneous abortion (miscarriage) can be estimated based on several medical studies. Infection at less than 20 weeks' gestation has about a 10 percent risk of fetal loss, while infection after 20 weeks has about a 1 percent fetal-loss rate.

Another complication that can occur in pregnancy is "hydrops fetalis." In this disorder, severe anemia in the fetus results in swelling of all fetal tissues. In about a third of cases, this may resolve without treatment. In other instances, the fetus may die. Data are conflicting on the risk of hydrops after maternal parvovirus infection, but the overall the risk seems to be low. Hydrops tends to occur later in pregnancy, while fetal loss without hydrops more often occurs earlier. There are also reports of many birth defects developing after parvovirus infection, but a cause-and-effect relationship has not been proven.

The medical approach to pregnant women exposed to the virus varies. I will give you one approach. Generally, diagnosing infection in pregnant women (and others) is accomplished by testing the blood for the presence of disease-fighting antibodies. This method will identify most women with a recent infection. If the infection is deemed to have occurred before 20 weeks' gestation, we would normally counsel the woman about the low risk of fetal loss and the lower risk of birth defects. No further intervention would be helpful or necessary.

If infection is deemed to occur after 20 weeks' gestation, then the main risk is hydrops fetalis. Sometimes, we can attempt to diagnose the condition by amniocentesis (withdrawing some amniotic fluid from the womb for testing). Usually, we do weekly ultrasound exams for four to eight weeks. If hydrops is identified, then the only possible treatment is to give the fetus a blood transfusion while still in the womb. (Experimental treatments exist, but they are poorly tested.) An intrauterine blood transfusion poses a definite risk of fetal death and should not be considered lightly, particularly since as many as one-third of all cases will of hydrops fetalis resolve without treatment. However, it does appear from some studies that this procedure, if done correctly, can prevent some fetal losses due to hydrops.