In a recent study published in American Journal of OtolaryngologyIn this study, researchers evaluated the impact of coronavirus disease 2019 (COVID-19) during pregnancy and the consequent effect on the auditory system of infants.
During pregnancy, infection with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) can significantly affect fetal development. Studies have noted a higher risk of maternal morbidity in pregnant women infected with SARS-CoV-2.
Furthermore, children born to women infected with COVID-19 during pregnancy showed a higher index of neonatal morbidity, increased acceptance of neonatal intensive care, and severe perinatal morbidity than infants born to mothers naïve to SARS-CoV-2 during pregnancy.
It is known that a viral infection during pregnancy can significantly affect the development of the auditory system. However, little is known about COVID-19 and its effects on newborn hearing. The integrity of the auditory system in newborns is measured by distortion-induced auditory emissions (DPOAEs) and the auditory brainstem response (ABR).
ABR is generated when a synapse forms or a sudden change in the axonal pathway occurs in the auditory brainstem and is characterized by peaks and valleys that can be recorded from individuals of all age groups. DPOAEs are generated within the cochlea in response to two converging frequencies of pure color, reflecting the state of the outer hair cells. The function of a person’s external hair cells is determined by comparing the amplitude of the DPOAE or signal-to-noise ratio (SNR) with the normative data.
Study and results
In the current study, the researchers performed a retrospective analysis of ABRs obtained from routine diagnostic follow-up and compared the ABRs of children born to women infected with COVID-19 during pregnancy (the COVID-19 group) with newborns of women who were negative for COVID-19 during pregnancy (controls). ).
Fifteen infants (10 males and five females) whose mothers contracted COVID-19 during pregnancy were identified from hospitals in southern Mississippi. There were 23 male and 17 female infants as controls. DPOAEs were registered for two primaries submitted simultaneously. Participants were included only if at least three f2 frequencies (out of six) generated an SNR of 6 dB or higher (dB). ABRs were recorded by delivering a rare 100-microsecond click at 23.5 per second. The stimuli were presented via monophonic input speakers of different intensities. Only absolute latencies (waves I, III, V) and interpeak periods (I to V) recorded at 70 dB (nHL) normal hearing levels were analysed. Statistical tests included the Mann-Whitney U tests and the Wilcoxon site rating test.
The authors found that the amplitude of DPOAE between the two groups was not significantly different as calculated using the Mann-Whitney U test and the Wilcoxon site classification test, indicating normal, functional external hair cells across all participants. The Wilcoxon site classification test showed no significant differences in absolute latency (I, III, V) in both test groups. However, only first wave response times were significant between test groups using the Mann-Whitney U test.
By contrast, the latency of the third and fifth wave was significantly prolonged in the COVID-19 infant group relative to the controls. While the Wilcoxon site classification test revealed that interpeak periods (I – V) were not significantly different for both test groups, the Mann-Whitney U test revealed significantly longer interpeak periods (I – V) in infants from the COVID-19 group compared to controls.
The current study recorded ABRs and DPOAEs in infants born to mothers who were infected with SARS-CoV-2 during pregnancy and to those born to mothers who were COVID-19-naive during pregnancy. The authors found that infants of the COVID-19 group had a DPOAE amplitude similar to healthy controls indicating normal cochlear functions in infants of the COVID-19 group.
While the results noted clicks of ABR thresholds at typical levels (20 dB nHL) and normal DPOAEs in both ears, ABRs at 70 dB nHL revealed significant delays in absolute latency (III and V waves) and interpeak periods between infants in the COVID-19 group. compared to the controls. This suggests that although COVID-19 infection during pregnancy may not necessarily be a risk factor for hearing loss, infants born to mothers infected with COVID-19 during pregnancy may show immature ABRs compared to controls.
These results indicate that COVID-19 during pregnancy can negatively affect the auditory system, which is still under development. While normal cochlear function is present, infants born to mothers exposed to COVID-19 during pregnancy may show neural delays to sound stimuli due to atypical neuronal or synaptic processes.
Furthermore, longitudinal studies are needed to study the maturation of the auditory system of these infants in the future.