CMV Testing in Pregnancy with Fetal Ventriculomegaly
Maternal Testing
Order maternal CMV IgG and IgM antibodies as the initial serologic test to determine infection status. 1, 2 If both IgG and IgM are positive, immediately add CMV IgG avidity testing to determine timing of maternal infection—high avidity indicates infection occurred >12-16 weeks prior, while low avidity suggests recent primary infection. 3, 4
Critical Pitfall to Avoid
Do not rely on negative maternal CMV IgM to rule out fetal CMV infection. 5 Congenital CMV can occur with maternal reactivation or reinfection in the absence of detectable IgM antibodies, particularly in cases presenting with fetal abnormalities like ventriculomegaly. 5, 6 The case series by Leruez-Ville demonstrates that fetal CMV infection can be confirmed even when maternal IgM is negative. 5
Fetal Testing
Perform amniocentesis for CMV DNA PCR (quantitative) to definitively diagnose fetal infection. 7, 4 This should be done at least 8 weeks after presumed maternal infection and after 17 weeks of gestation to maximize sensitivity. 6 The amniocentesis provides direct evidence of fetal infection with high sensitivity and specificity. 4
Timing Considerations
- Wait at least 8 weeks after suspected maternal infection before amniocentesis 6
- At 24 weeks gestation with fetal abnormalities already present, amniocentesis can be performed immediately if maternal infection timing is uncertain 4
- CMV DNA PCR on amniotic fluid is the gold standard for prenatal diagnosis 4, 6
Additional Fetal Evaluation
Order detailed fetal MRI of the brain at 28-32 weeks gestation to assess for CMV-related brain injury. 4 MRI provides superior detection of subtle brain abnormalities compared to ultrasound, particularly white matter changes, polymicrogyria, and periventricular calcifications that are characteristic of CMV. 1, 4 In cases of complex ventriculomegaly, MRI provides additional clinically useful information in 78.2% of cases. 8
Schedule serial ultrasound examinations every 2-3 weeks until delivery to monitor for progression of findings. 4 These should include detailed assessment of:
- Ventricular size progression 4
- Development of periventricular hyperechogenicity or calcifications 1, 9
- Fetal growth parameters 4
- Development of hydrops fetalis (CMV accounts for 5-10% of nonimmune hydrops) 1
Genetic Testing Considerations
Offer chromosomal microarray analysis (CMA) via amniocentesis when fetal malformations are present. 7 In cases of complex ventriculomegaly with additional structural abnormalities, genetic testing identifies chromosomal abnormalities in 26.7% of cases. 8 This can be performed on the same amniocentesis sample as CMV testing. 7
Testing NOT Recommended
Do not routinely screen for toxoplasmosis, rubella, or herpes in the absence of specific risk factors. 7 While these infections can cause similar fetal brain abnormalities, maternal serologic screening for these pathogens has extremely low yield without documented exposure or acute illness. 7, 3 Focus testing on CMV given the ultrasound findings of ventriculomegaly, small cisterna magna, and thin nuchal fold—a constellation highly suggestive of congenital CMV. 1, 9
Rationale for CMV-Focused Approach
The combination of bilateral ventriculomegaly with cisterna magna abnormality represents a pattern characteristic of CMV infection. 1, 9 One case report documented rapid progression of CMV findings from isolated echogenic bowel to bilateral ventriculomegaly with periventricular changes within just 5 days. 9 This underscores both the aggressive nature of CMV and the importance of timely, focused testing rather than broad infectious screening. 9
Summary Algorithm
- Immediate maternal testing: CMV IgG + IgM (add avidity if both positive) 1, 2, 3
- Fetal diagnostic testing: Amniocentesis for CMV DNA PCR 4, 6
- Genetic evaluation: CMA on same amniocentesis sample 7, 8
- Advanced imaging: Fetal brain MRI at 28-32 weeks 4, 8
- Ongoing surveillance: Ultrasound every 2-3 weeks until delivery 4