COVID-19 in pregnancy tied to higher preterm birth risk; early vaccine adoption shows protective effect

A study published in PNAS describes the impact of maternal coronavirus disease 2019 (COVID-19) infection on infant health and the importance of vaccination in mitigating negative health outcomes in infants.

Study: Vaccination, immunity, and the changing impact of COVID-19 on infant health. Image Credit: Andrii Vodolazhskyi/


The COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has mostly and severely affected elderly people, immunocompromised patients, and those with comorbidities. However, growing evidence suggests that the virus can negatively impact maternal and infant health.

During pregnancy, in utero exposure of infants to SARS-CoV-2 may lead to significant intergenerational health consequences. New viral variants that have emerged throughout the pandemic may have a distinct effect on infant health.

On the other hand, immunity developed from previous SARS-CoV-2 infection or COVID-19 vaccination may protect infant health.

In this study, scientists have explored the changing impact of maternal COVID-19 on preterm birth and the protective efficiency of COVID-19 vaccination in mitigating this effect. 

Study design

The impact of maternal SARS-CoV-2 infection during pregnancy on preterm birth risk was investigated in this study using population-level data on maternal SARS-CoV-2 infection and the linked population-level data on infants born between 2014 and 2023 in birth facilities in California, US. The general population of this state accounts for approximately 12% of all births in the US.

Being the main predictor of infant morbidity and mortality in the US, preterm birth influences long-term markers of well-being, including educational and socioeconomic status.

Considering its significance in population health, intergenerational health, and socioeconomic disparities, preterm birth was selected as a marker of infant health in this study.  

Important observations

The analysis of the average impact of maternal COVID-19 on preterm birth over the period of 2020 to 2023 revealed that maternal infection at the time of delivery can increase the risk of preterm birth by 29%.

This estimation was obtained after adjusting for potential birth facility confounders (differences in COVID-19 testing protocols, labor and delivery protocols, and socioeconomic status of patients) and time-of-birth confounders (trends in COVID-19 infection and temporal changes in testing shared across facilities).

A separate set of analyses conducted after adjusting for a wide range of observed maternal sociodemographic and risk factors revealed a 15% increase in the risk of preterm birth if the mother has SARS-CoV-2 infection at the time of delivery.

Changing impact of maternal SARS-CoV-2 infection on infant health

Over time, a gradual change in COVID-19 health impact has been observed throughout the pandemic.

This could be because of changing infectivity and pathogenicity of new viral variants, as well as the development of herd immunity from previous SARS-CoV-2 infection or COVID-19 vaccination. 

Analysis of the changing impact of maternal COVID-19 over time revealed a 78% increase in the risk of preterm birth during the earliest phase of the pandemic (July 2020 to December 2020).

A fluctuation in the preterm birth risk due to maternal COVID-19 was observed during the delta variant-dominated wave in 2021. A complete disappearance of the health impact of maternal infection was observed in 2022, including the period of the omicron-dominated wave.

In California, around 70% of the entire population was vaccinated against COVID-19 by March 2022. However, a significant variation in vaccine uptake rate was observed across the state. While vaccination rate of 86% was achieved in some regions, it reached a maximum of only 51% in some regions.

The comparison of the impact of maternal COVID-19 based on vaccination rates revealed that the negative infant health impact of COVID-19 completely disappeared almost a year earlier in regions with the highest vaccine uptake compared to the regions with the lowest vaccine uptake.

Study significance

The study finds that maternal SARS-CoV-2 infection during pregnancy can increase the risk of preterm birth, which is associated with many long-term health adversities in infants.

The study also highlights the protective effects of COVID-19 vaccines in mitigating harmful consequences associated with maternal COVID-19.

The largest impact of maternal infection on preterm birth was observed during the earliest phase of the pandemic. This highlights the absence of anti-COVID-19 immunity in the general population because of the unavailability of therapeutics and vaccines.

With increasing vaccine uptake, an initial decline and subsequent disappearance of the impact of maternal infection was observed. This highlights the potential protective efficacy of COVID-19 vaccination.

Journal reference:
  • Torche F. (2023). Vaccination, immunity, and the changing impact of COVID-19 on infant health. PNAS. doi:

Posted in: Child Health News | Medical Science News | Medical Research News | Disease/Infection News

Tags: Coronavirus, covid-19, Efficacy, immunity, In Utero, Labor, Mortality, Omicron, Pandemic, Pregnancy, Respiratory, SARS, SARS-CoV-2, Severe Acute Respiratory, Severe Acute Respiratory Syndrome, Syndrome, Therapeutics, Vaccine, Virus

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Written by

Dr. Sanchari Sinha Dutta

Dr. Sanchari Sinha Dutta is a science communicator who believes in spreading the power of science in every corner of the world. She has a Bachelor of Science (B.Sc.) degree and a Master's of Science (M.Sc.) in biology and human physiology. Following her Master's degree, Sanchari went on to study a Ph.D. in human physiology. She has authored more than 10 original research articles, all of which have been published in world renowned international journals.