Diagnosing CMV infection
Maternal infection
If maternal CMV infection is suspected based on a symptomatic illness or an abnormal fetal ultrasound exam, the first diagnostic test should be an assessment of IgM and IgG serology. If the former test results are positive and the latter negative, the diagnosis of acute CMV infection is confirmed. A positive serum CMV DNA polymerase chain reaction (PCR) test adds additional assurance that the diagnosis is correct. Primary infection, as noted above, poses the greatest risk of serious injury to the fetus.1
A frequent diagnostic dilemma arises when both the IgM and IgG antibody are positive. Remember that CMV IgM antibody can remain positive for 9 to 12 months after a primary infection and can reappear in the maternal serum in the face of a recurrent or reactivated infection. When confronted by both a positive IgM and positive IgG result, the clinician should then order IgG avidity testing. If the avidity is low to moderate, which reflects poor binding of antibody to the virus, the patient likely has an acute infection. If the avidity is high, which reflects enhanced binding of antibody to virus, the patient probably has a recurrent or reactivated infection; this scenario poses less danger to the developing fetus. The presence of CMV DNA in serum is also more consistent with acute infection, although viremia still can occur with recurrent infection. FIGURE 2 presents a suggested algorithm for the diagnosis of CMV in the pregnant patient.1
If a diagnosis of maternal CMV infection is confirmed, liver function tests should be obtained to determine if CMV hepatitis is present. If the liver function tests are abnormal, a coagulation profile also should be performed to identify the mother who might be at risk for peripartum hemorrhage.
Fetal infection
The single best test for confirmation of congenital CMV infection is detection of viral DNA and quantitation of viral load in the amniotic fluid by PCR. If the amniocentesis is performed prior to 20 weeks’ gestation and is negative, the test should be repeated in approximately 4 weeks.1,19,24
Detection of viral DNA indicates congenital infection. The ultimate task, however, is to determine if the infection has injured the fetus. Detailed ultrasound examination is the key to identifying fetal injury. As noted previously, the principal ultrasonographic findings that suggest congenital CMV infection include2,19,20,21,25:
- hydropic placenta
- fetal growth restriction
- microcephaly (head circumference more than 3 standard deviations below the mean)
- periventricular calcifications
- enlarged liver
- echogenic bowel
- ascites
- fetal hydrops.
Management: Evidence on CMV hyperimmune globulin, valacyclovir
If the immunocompetent mother has clinical manifestations of infection, she should receive symptomatic treatment. She should be encouraged to rest as much as possible, stay well hydrated, and use acetaminophen (1,000 mg every 6 to 8 hours) as needed for malaise and fever.
However, if the mother is immunocompromised and has signs of serious complications, such as chorioretinitis, hepatitis, or pneumonia, more aggressive therapy is indicated. Drugs used in this setting include foscarnet and ganciclovir and are best prescribed in consultation with a medical infectious disease specialist.
At this time, no consistently effective therapy for congenital infection is available. Therefore, if a patient has primary CMV infection in the first half of pregnancy, particularly in the first trimester, she should be counseled that the risk of fetal infection is approximately 40% and that approximately 5% to 15% of infants will be severely affected at birth. Given this information, some patients may opt for pregnancy termination.
In 2005, a report from Nigro and colleagues stimulated great hope that CMV-specific hyperimmune globulin (CytoGam) might be of value for both treatment and prophylaxis for congenital infection.26 These authors studied 157 women with confirmed primary CMV infection. One-hundred forty-eight women were asymptomatic and were identified by routine serologic screening, 8 had symptomatic infection, and 1 was identified because of abnormal fetal ultrasound findings. Forty-five women had CMV detected in amniotic fluid by PCR or culture more than 6 weeks before study enrollment. Thirty-one of these women were treated with intravenous hyperimmune globulin (200 U or 200 mg/kg maternal body weight); 14 declined treatment. Seven of the latter women had infants who were acutely symptomatic at the time of delivery; only 1 of the 31 treated women had an affected neonate (adjusted odds ratio [OR], 0.02; P<.001). In this same study, 84 women did not have a diagnostic amniocentesis because their infection occurred within 6 weeks of enrollment, their gestational age was less than 20 weeks, or they declined the procedure. Thirty-seven of these women received hyperimmune globulin (100 U or 100 mg/kg) every month until delivery, and 47 declined treatment. Six of the treated women delivered infected infants compared with 19 of the untreated women (adjusted OR, 0.32; P<.04).
Although these results were quite encouraging, several problems existed with the study’s design, as noted in an editorial that accompanied the study’s publication.27 First, the study was not randomized or placebo controlled. Second, patients were not stratified based on the severity of fetal ultrasound abnormalities. Third, the dosing of hyperimmune globulin varied; 9 of the 31 patients in the treatment group received additional infusions of drug into either the amniotic fluid or fetal umbilical vein. Moreover, patients in the prophylaxis group actually received a higher cumulative dose of hyperimmune globulin than patients in the treatment group.
Two subsequent investigations that were better designed were unable to verify the effectiveness of hyperimmune globulin. In 2014, Revello and colleagues reported the results of a prospective, randomized, placebo-controlled, double-blinded study of 124 women at 5 to 26 weeks’ gestation with confirmed primary CMV infection.28 The rate of congenital infection was 30% in the group treated with hyperimmune globulin and 44% in the placebo group (P=.13). There also was no significant difference in the concentration of serum CMV DNA in treated versus untreated mothers. Moreover, the number of adverse obstetric events (preterm delivery, fetal growth restriction, intrahepatic cholestasis of pregnancy, and postpartum preeclampsia) in the treatment group was higher than in the placebo group, 13% versus 2%.
In 2021, Hughes and colleagues published the results of a multicenter, double-blind trial in 399 women who had a diagnosis of primary CMV infection before 23 weeks’ gestation.29 The primary outcome was defined as a composite of congenital CMV infection or fetal/neonatal death. An adverse primary outcome occurred in 22.7% of the patients who received hyperimmune globulin and 19.4% of those who received placebo (relative risk, 1.17; 95% confidence interval [CI], 0.80–1.72; P=.42).
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