SARS-CoV-2 infection found to reduce fetal lung volume as assessed by MRI

By Pooja Toshniwal PahariaReviewed by Aimee MolineuxMar 21 2022

In a recent study published in The Lancet Respiratory Medicine, researchers evaluated the impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in gestational women on fetal pulmonary development using magnetic resonance imaging (MRI).

Coronavirus disease 2019 (COVID-19) can cause several acute disorders with long-term effects. Pulmonary health has remained a key concern owing to the high SARS-CoV-2 affinity for the respiratory alveolar cells. Previous studies have reported on the SARS-CoV-2-induced maternal placental changes and vertical transmission to the fetus during pregnancy; however, the long-term consequences of COVID-19 on fetal pulmonary health have not yet been determined.

About the study

In the present study, researchers evaluated the effects of SARS-CoV-2 infection on fetal pulmonary growth. They assessed the fetal lung volume using MRI as an indicator of lung development in neonates born to SARS-CoV-2-positive women. These lung volumes were described as a percentage of the 50th percentile reference values. The team analyzed MRI scans of 34 gestational women (at 33.5 weeks of gestation) who had polymerase chain reaction (PCR)-confirmed mild and uncomplicated SARS-CoV-2 infections.

The impact of the pregnancy period at the time of MRI scanning, time point (trimester), sex, and the period of infection on the fetal lung volumes were evaluated using a generalized linear model with identity linking functionalities. Thrombosis and placental heterogeneity were given scores ranging from zero (none) to four (severe). Additionally, the birth weight of neonates was measured on follow-up visits. Neonatal oxygen saturation was monitored using pulse oximetry. The appearance, pulse, grimace, activity, and respiration (Apgar) scores were used to describe the infant’s health immediately after birth.

Results

In gestational SARS-CoV-2-positive women, fetal lung volumes were significantly diminished when compared with the age-adjusted 50th percentile reference values. Organ infarctions or structural anomalies were absent in the fetus. Additionally, the pulmonary volumes were most significantly reduced during the final trimester of pregnancy (69% versus 91% of the 50th percentile reference values in the second or first trimester). However, the periods of infection and pregnancy at the time of MRI scanning, and sex did not significantly affect fetal pulmonary development.

The diminution of normalized lung volumes was underpinned on masked comparison with an area-specific control group of 15 healthy pregnant women negative for SARS-CoV-2 (95% versus 69% of the 50th percentile reference values with COVID-19 in the final trimester), and analysis by another reader.

Compared to the controls, SARS-CoV-2-positive pregnant women demonstrated enhanced heterogeneity of placental and thrombotic alterations. However, the normalized lung volumes were not significantly associated with the placental alterations considering the pregnancy period at the time of MRI scanning.

Follow-up neonatal assessments in 21 of 34 newborns (62%) showed normal birth weight at 35 to 42 weeks of gestation without any signs of acute postpartum pulmonary dysfunction. Additionally, the neonatal oxygen saturation levels were 97% to 100%, and the Apgar scores ranged between 9 and 10.

Conclusion

According to the authors, the present study is the first report on diminished fetal pulmonary volume in SARS-CoV-2-positive pregnant women. This diminution depended on the time point of COVID-19 with the most profound impact observed in the final trimester of pregnancy. This third or final trimester corresponds to the saccular phase of pulmonary development in which the air cavities of the lungs enlarge.  

Despite ambiguous observations on placental vertical transmission, the predominant spread of infection in the final trimester, and significant correlations between the SARS-CoV-2 amniotic presence and positive PCR results close to delivery could increase the viral exposure of the evolving lung tissues, facilitated by higher respiratory fetal rates in the final trimester. Particularly, the high viral affinity for the pulmonary alveolar epithelial cells could cause significant effects on their development.

There were no signs of postpartum pulmonary dysfunction in the neonates of SARS-CoV-2-positive pregnant women. This highlights a prenatal SARS-CoV-2 exposure-related phenotype that must be structurally and functionally addressed in further studies that assess fetal exposure to hazards such as toxins and infections.

Furthermore, the present study results support the administration of SARS-CoV-2 vaccines to pregnant women.