Diagnostic steps
Appropriate diagnostic evaluation for a pregnant woman with exposure to parvovirus or clinical manifestations suggestive of parvovirus infection is outlined in FIGURE 1.
If infection is confirmed, serial ultrasound monitoring should be performed on a weekly to biweekly basis for 8 to 12 weeks, as delineated in FIGURE 2. Extended surveillance is necessary because the incubation period in the fetus is longer than that in the mother.
As the fetus develops anemia, peripheral tissues become hypoxic, leading to reflex peripheral vasoconstriction and increased cardiac output. At the same time, reduction in the number of fetal red blood cells decreases blood viscosity. The combination of these changes results in an increase in blood flow to the fetal brain, which can be detected by measuring the peak systolic velocity of flow in the middle cerebral artery (MCA PSV) with Doppler ultrasound imaging (FIGURE 3). The increase in MCA PSV parallels the decrease in fetal hematocrit and precedes the development of hydrops. In fact, signs of fetal hydrops do not usually develop until the fetal hematocrit falls to 15 to 20 vol%.
Management may necessitate intrauterine transfusion
Although some cases of fetal hydrops may resolve spontaneously, most authors agree that intrauterine transfusion is essential. In most instances, only a single intrauterine transfusion is necessary. In some fetuses, however, the infection is so prolonged and the anemia so severe that 2 to 3 transfusions may be required.
Infants who survive the intrauterine transfusion usually have an excellent long-term prognosis. However, isolated case reports have documented neurologic morbidity and prolonged transfusion-dependent anemia.4 In light of these reports, we recommend that a third trimester ultrasound exam be performed to assess fetal growth and evaluate the anatomy of the fetal brain. For the fetus with abnormal intracranial findings on ultrasonography, fetal magnetic resonance imaging is indicated.5
CASE #1 Diagnosis is probable parvovirus
The most likely diagnosis in this case is erythema infectiosum. This diagnosis can be confirmed by identifying positive immunogloblulin M (IgM) antibody and by detecting parvovirus in the maternal serum by polymerase chain reaction. Given the gestational age of 16 weeks, the risk of serious fetal injury should be less than 5%. Nevertheless, serial ultrasound examinations should be performed to assess for signs of fetal anemia.
Varicella exposure in pregnancy
CASE #2 Pregnant woman exposed to chickenpox has symptoms
Two weeks ago, a 32-year-old woman (G3P2002) at 24 weeks’ gestation was exposed to a neighbor’s child who had chickenpox. The patient has no history of natural infection or vaccination. She now has a fever of 38.6°C, malaise, headache, and a diffuse pruritic vesicular rash on her trunk and extremities. She also is experiencing a dry cough and mild dyspnea.
- What diagnostic tests are indicated?
- What treatment is indicated?
- What risk does this condition pose to the fetus?
Epidemiology of varicella
Varicella (chickenpox) is caused by the DNA varicella-zoster virus, an organism that is a member of the herpesvirus family. The disease occurs predominantly in children, and the infection is transmitted by respiratory droplets and by direct contact. Its incubation period is short (10–14 days), and it is highly contagious. More than 90% of susceptible close contacts will become infected after exposure to the index case. Like other herpesviruses, the varicella virus can establish a latent infection and then become manifest years later as herpes zoster (shingles).5,6
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