Evaluation of Fetal Lung Development via MRI During Omicron SARS-CoV-2 Phase
Overview
This prospective cohort study assessed fetal lung volumes via MRI in 24 pregnant women with mild SARS-CoV-2 infection during the omicron-dominated phase. Results showed fetal lung volumes comparable to age-adjusted reference values and non-COVID controls, contrasting with earlier findings from the alpha variant phase.
Background
Early in the COVID-19 pandemic, fetal MRI revealed reduced lung volumes in offspring of women infected with the alpha variant of SARS-CoV-2. The omicron variant, characterized by higher transmissibility but lower lower respiratory tract involvement, has been associated with milder disease and improved perinatal outcomes. Vaccination and hybrid immunity became widespread during the omicron phase, potentially influencing fetal development. Investigating fetal lung growth during this period is critical to understanding variant- and immunity-related effects on pregnancy outcomes.
Data Highlights
Parameter
Omicron SARS-CoV-2 Group (n=24)
Non-COVID Controls (n=15)
Median Gestational Age at MRI (weeks)
33.3 (range 24–38)
29.7 (range 24–35)
Vaccination Status
20 with 3 doses, 2 with 2 doses, 2 unvaccinated
Not applicable (pre-pandemic)
Median Time from Infection to MRI (days)
74.3 (range 12–153)
Not applicable
Severity of Maternal COVID-19
Mild symptoms only
Not applicable
Fetal Lung Volume
Comparable to age-adjusted references and controls
Baseline reference values
Key Findings
Fetal lung volumes in pregnancies affected by mild omicron SARS-CoV-2 infection were not reduced compared to non-COVID controls.
Most women (83%) were triple vaccinated prior to infection, suggesting hybrid immunity during the omicron phase.
Infections occurred predominantly in the second trimester (67%), with median MRI performed at 33.3 weeks gestation.
All maternal infections were mild, with common symptoms including fatigue, headache, and upper respiratory symptoms.
Fetal MRI acquisition and lung volume segmentation were performed blinded and showed high inter-reader reliability.
Findings contrast with earlier alpha variant data showing reduced fetal lung volumes, indicating variant-specific and immunity-related effects on fetal lung development.
Clinical Implications
These findings suggest that mild maternal infection with the omicron variant, especially in the context of vaccination and hybrid immunity, does not adversely affect fetal lung growth as measured by MRI. This supports the safety of current vaccination policies in pregnancy and may reassure clinicians and patients regarding fetal pulmonary development during mild omicron infections. Continued monitoring and imaging may be warranted in cases of more severe maternal disease or different variants.
Conclusion
Fetal lung development assessed by MRI during the omicron-dominated phase of the pandemic appears preserved in mild maternal SARS-CoV-2 infection, contrasting with earlier alpha variant findings. This highlights the impact of viral variant characteristics and maternal immunity on fetal outcomes.
References
Köhler et al. 2021 -- Reduced fetal lung volume after maternal SARS-CoV-2 infection
Hoffmann et al. 2022 -- SARS-CoV-2 variant tropism and entry mechanisms
Meng et al. 2022 -- Omicron variant characteristics and transmissibility
European CDC 2022 -- COVID-19 vaccination recommendations for pregnant women
Smith et al. 2023 -- Placental changes in omicron versus pre-omicron infections
by Gloria Biechele, Vanessa Koliogiannis, Philippe Rennollet, Tobias Prester, Enrico Schulz, Thomas Kolben, Magdalena Jegen, Christoph Hübener, Uwe Hasbargen, Andreas Flemmer, Olaf Dietrich, Tanja Burkard, Regina Schinner, Julien Dinkel, Maximilian Muenchhoff, Susan Hintz, Maria Delius, Sven Mahner, Jens Ricke, Anne Hilgendorff, Sophia Stoecklein
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