In a recent study published in Clinical Infectious Diseases, researchers assessed the severity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections during pregnancy in Ontario, Canada.

Study: Severity of SARS-CoV-2 Infection in Pregnancy in Ontario: A Matched Cohort Analysis. Image Credit: M M Vieira/Shutterstock
Study: Severity of SARS-CoV-2 Infection in Pregnancy in Ontario: A Matched Cohort Analysis. Image Credit: M M Vieira/Shutterstock

Studies have reported that pregnant women and their developing infants are at an increased risk of severe infectious diseases. The coronavirus disease 2019 (COVID-19) pandemic could have essential health implications for expecting women, who may also demonstrate an increased reluctance to vaccinations compared to non-pregnant women.

About the study

In the present study, researchers assessed the impact of COVID-19 severity on pregnancy outcomes in Ontario.

The study was conducted between 1 January 2020 and 4 January 2022 to determine the relative risk of severe COVID-19 among SARS-CoV-2-positive pregnant females (cases) and SARS-CoV-2-positive females of reproductive age (or controls, aged between 10 years and 49 years). A SARS-CoV-2 case file based on the population of Ontario was used for the analysis.

The controls were matched to the SARS-CoV-2-positive pregnant females by SARS-CoV-2-positive laboratory test dates. Pregnant women and time-matched control female-identified from the case and contact management (CCM) database of Ontario were analyzed. In addition, data on COVID-19 vaccination of the case group women and control group women were obtained from the COVaxON dataset of Ontario, which included data on vaccination type and doses administered.

The impact of comorbidities such as asthma, cancer, obesity, neurological disorders, renal disorders, hematological disorders, cardiovascular disorders, and hepatic disorders on the hospitalization risks was assessed for the two groups. Further, the person-time at SARS-CoV-2 infection risk was estimated for the study participants based on 107,855 and 482 reported live births and stillbirths, respectively, among reproductive-age women residing in Ontario between 1 January and 31 October 2021.

Conditional and multivariable logistic regression modeling was used for determining the comparative risk of severe COVID-19 outcomes among the two study groups. Standardized morbidity ratios (SMRs) and adjusted odds ratios (aORs) were calculated for the analysis. In addition, a restriction analysis was performed to evaluate the risk of ICU admissions among hospitalized cases and controls with data adjustments for vaccination, age, and comorbidities.

Results and discussion

A total of 11,257 and 2,252 females belonging to the control group and case group, respectively, were analyzed. Non-pregnant and reproductive age females demonstrated a greater risk of infection compared to pregnant females with SMR values of 1.3 and 0.4, respectively. After making data adjustments for confounding variables, pregnant females were substantially more prone to hospital admissions (adjusted OR 4.9) and intensive care unit (ICU) admissions (adjusted OR 6.6).

Further, the relative increases in pregnancy-associated hospital admission risks were higher among women with negative history of comorbid conditions compared to women with comorbid conditions. Cases and controls differed substantially in terms of risks of hospital admissions and ICU admissions, age, the status of vaccination, and comorbidities.  Diabetes, asthma, and hematological disorders were more prevalent among cases; however, no differences were observed among cases and controls in terms of the causative SARS-CoV-2 variants.

Substantially higher risks of hospital admissions (aOR 4.9) and ICU admissions (aOR 6.6) were observed among cases in comparison to controls; however, the differences between the above-mentioned risks among cases and controls were non-significant after data adjustments for age, the status of vaccination, causative SARS-CoV-2 variant and comorbidities (aOR = 1.3).

The restricted analysis showed that the chances of hospital admissions were substantially higher among cases without comorbid conditions (aOR 5.6) than those with comorbid conditions (aOR 2.3). No heterogeneity was observed for ICU admission risks based on comorbidities and for the impact of pregnancy based on the causative SARS-CoV-2 variants and status of vaccination.

Further, a lower risk of ICU admission was not observed for pregnant women hospitalized due to COVID-19 in comparison to those hospitalized for other reasons, indicating an increased likelihood of pregnant women being hospitalized for severe pulmonary disorders instead of simply COVID-19 monitoring.

Moreover, the increase in pregnancy-associated risks was less prominent when restricting the analysis to cases and controls with comorbidities, indicating that among otherwise healthy females, pregnancy itself can be considered a factor for increased COVID-19 severity, whereas among females with comorbidities, pregnancy is only one of several other risk-augmenting factors.  

Studies have reported higher cardiovascular demands and reduced respiratory reserve in pregnancy along with physiological immune impairments, and such changes have been associated with worsened pulmonary infection outcomes. Further, several hematological and vascular pathological alterations occur in COVID-19, which increase the risk of stillbirths among SARS-CoV-2-positive women.


Overall, the study findings showed that pregnant women were at increased risk of COVID-19 severity compared to non-pregnant women of reproductive age, although the risk of COVID-19 was relatively lower among pregnant women. Considering COVID-19 vaccines’ safety among pregnant women, the study findings are in favor of COVID-19 vaccinations during pregnancy. The lower risk of SARS-CoV-2 infections among cases could be due to stricter adherence to health guidance protocols and/or avoidance of high-risk settings of SARS-CoV-2 transmission.

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