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Background <p>Accurate diagnosis of primary cytomegalovirus infection (CMV PI) during pregnancy is critical for prognosis and clinical management, yet CMV-IgM may be transient or absent in the early phase of infection, leading to underdiagnosis. We aimed to determine the frequency and characteristics of negative or equivocal CMV-IgM results observed in confirmed recent CMV PI and to assess whether this diagnostic pitfall could be reduced.</p> Methods <p>We retrospectively analysed 1,090 cases of CMV PI occurring within 2 months of infection onset in pregnant women referred to the French National Reference Laboratory for Viral Perinatal Infections between 2013 and 2025. CMV-IgG, CMV-IgM, and CMV-IgG avidity were assessed using the LIAISON<sup>®</sup> XL platform, with additional avidity testing on VIDAS<sup>®</sup>. Recent infection was defined by IgG seroconversion and/or low IgG avidity (&lt; 30% on VIDAS). We analysed the frequency, timing, and characteristics of negative or equivocal CMV-IgM results and evaluated the potential impact of pragmatic interpretation criteria.</p> Results <p>Among 1,090 cases of early CMV PI, 2.6% (28/1,090) had negative or equivocal CMV-IgM results, including 1.7% (18/1,090) negative and 0.9% (10/1,090) equivocal results. CMV-IgM negativity was observed both within the first month [1.4% (9/664)] and between 1 and 2 months [2.1% (9/426)] after the onset of infection. Among IgM-negative patients, 39% (7/18) had low CMV-IgG levels on LIAISON<sup>®</sup> XL (&lt; 28 U/mL), consistent with very early seroconversion. In contrast, 61% (11/18) had CMV-IgG levels above twice the positivity threshold (&gt; 28 U/mL), mimicking past immunity and representing a true diagnostic blind spot, accounting for 1.0% (11/1,090) of all infections. Considering CMV-IgM values between 15 and 18 U/mL as low-reactive results requiring further assessment, together with repeat serology when CMV-IgG levels were below twice the positivity threshold, would have reclassified 14 of 18 IgM-negative cases and reduced missed diagnoses from 1.7% (18/1,090) to 0.4% (4/1,090).</p> Conclusion <p>Two complementary measures may improve detection of CMV-IgM-negative early infections while maintaining a manageable laboratory workload: repeat serology when CMV-IgG levels are very low, and further assessment of low-reactive CMV-IgM values between 15 and 18 U/mL. Nevertheless, a small residual diagnostic gap remains, highlighting the inherent limitations of CMV-IgM-based screening for recent CMV infection during pregnancy.</p>

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Maternal early primary CMV infection with negative or equivocal CMV IgM

  • 期刊论文

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  • 发表日期：

    2026年4月28日

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  • Vincent Portet Sulla,
  • Rana Rafek,
  • Elise Bouthry,
  • Aude Simas,
  • Abir Jadaoui,
  • Lina Mouna,
  • Claire Perillaud-Dubois,
  • Christelle Vauloup-Fellous

摘要

Background

Accurate diagnosis of primary cytomegalovirus infection (CMV PI) during pregnancy is critical for prognosis and clinical management, yet CMV-IgM may be transient or absent in the early phase of infection, leading to underdiagnosis. We aimed to determine the frequency and characteristics of negative or equivocal CMV-IgM results observed in confirmed recent CMV PI and to assess whether this diagnostic pitfall could be reduced.

Methods

We retrospectively analysed 1,090 cases of CMV PI occurring within 2 months of infection onset in pregnant women referred to the French National Reference Laboratory for Viral Perinatal Infections between 2013 and 2025. CMV-IgG, CMV-IgM, and CMV-IgG avidity were assessed using the LIAISON® XL platform, with additional avidity testing on VIDAS®. Recent infection was defined by IgG seroconversion and/or low IgG avidity (< 30% on VIDAS). We analysed the frequency, timing, and characteristics of negative or equivocal CMV-IgM results and evaluated the potential impact of pragmatic interpretation criteria.

Results

Among 1,090 cases of early CMV PI, 2.6% (28/1,090) had negative or equivocal CMV-IgM results, including 1.7% (18/1,090) negative and 0.9% (10/1,090) equivocal results. CMV-IgM negativity was observed both within the first month [1.4% (9/664)] and between 1 and 2 months [2.1% (9/426)] after the onset of infection. Among IgM-negative patients, 39% (7/18) had low CMV-IgG levels on LIAISON® XL (< 28 U/mL), consistent with very early seroconversion. In contrast, 61% (11/18) had CMV-IgG levels above twice the positivity threshold (> 28 U/mL), mimicking past immunity and representing a true diagnostic blind spot, accounting for 1.0% (11/1,090) of all infections. Considering CMV-IgM values between 15 and 18 U/mL as low-reactive results requiring further assessment, together with repeat serology when CMV-IgG levels were below twice the positivity threshold, would have reclassified 14 of 18 IgM-negative cases and reduced missed diagnoses from 1.7% (18/1,090) to 0.4% (4/1,090).

Conclusion

Two complementary measures may improve detection of CMV-IgM-negative early infections while maintaining a manageable laboratory workload: repeat serology when CMV-IgG levels are very low, and further assessment of low-reactive CMV-IgM values between 15 and 18 U/mL. Nevertheless, a small residual diagnostic gap remains, highlighting the inherent limitations of CMV-IgM-based screening for recent CMV infection during pregnancy.