Preserved prenatal lung growth assessed by fetal MRI in the omicron-dominated phase of the SARS-CoV-2 pandemic.

Objectives: With SARS-CoV-2 evolving, disease severity and presentation have changed due to changes in mechanisms of entry and effector site as well as due to effects of vaccination- and/or infection-acquired immunity. We re-assessed fetal lung pathology in pregnancies with uncomplicated SARS-CoV-2 infections during the late, omicron-dominated pandemic phase to inform disease understanding and pregnancy consultation.

Methods: In this case-control study, fetal lung volumes were assessed by fetal MRI in 24 pregnancies affected by mild maternal SARS-CoV-2 infection during the omicron-dominated pandemic phase with prevailing immunity through vaccination and/or prior SARS-CoV-2 infection.

Results: Fetal lung volumes (normalized to estimated fetal weight) in 24 pregnancies (GA 33.3 ± 3.8, 12 female fetuses) following mild, uncomplicated SARS-CoV-2 infection did not differ significantly from both, published reference values (96.3% ± 22.5% of 50th percentile reference values, p = 0.43), or fetal lung volumes of a site-specific, non-COVID control group (n = 15, 94.2% ± 18.5%, p = 0.76). Placental assessment revealed no group differences in thrombotic changes or placental heterogeneity (p > 0.05, respectively), and fetal lung volume did not correlate with placental heterogeneity when adjusting for gestational age at scan (p > 0.05).

Conclusion: Assessment of fetal lung volume by MRI revealed unaffected lung growth in pregnancies affected by uncomplicated SARS-CoV-2 infection in the omicron-dominated pandemic phase in the presence of prevailing hybrid immunity. This finding contrasts sharply with the observed reduction in fetal lung volume following maternal alpha-variant infection in the pre-vaccination era and might reflect tropism- as well as immunity-related effects.

Key points: Question: Is fetal lung development affected by mild maternal SARS-CoV-2 infection during the omicron-dominated phase of the pandemic?

Findings: Fetal lung volume in 24 affected pregnancies did not differ significantly from published reference values or fetal lung volumes in 15 site-specific, non-COVID-affected control pregnancies.

Clinical relevance: Preserved fetal lung volume following mild maternal SARS-CoV-2 infection during the omicron-dominated phase contrasts with previous findings of reduced volume in unvaccinated pregnancies during the alpha-dominated pandemic phase. These observations might reflect tropism- as well as immunity-related effects.