Metastudy of pregnant women reveals risk factors for COVID-19

Some studies have suggested that pregnant women are at greater risk of serious complications associated with coronavirus disease 2019 (COVID-19) than non-pregnant women. In a paper recently uploaded to the preprint server medRxiv*, the influence of pregnancy on SARS-CoV-2 infection outcomes was assessed on a wide scale, potentially informing future public messaging and COVID-19 prevention strategies.

Study: Risk factors for illness severity among pregnant women with confirmed SARS-CoV-2 infection – Surveillance for Emerging Threats to Mothers and Babies Network, 20 state, local, and territorial health departments, March 29, 2020 -January 8, 2021. Image Credit: PH888 / Shutterstock

How was the study performed?

The group examined 5,963 CDC patient records collected between the period March 29, 2020, to January 8, 2021, related to pregnant women, categorizing the severity of COVID-19 illness alongside demographic information and medical history. Information including age, ethnicity, health insurance status and the existence of pre-existing medical conditions was cumulated to compare pregnant women with no such conditions to those with any one, two, or three underlying conditions, with or without SARS-CoV-2 infection.

This allowed the group to construct a risk ratio accounting for each of these factors relevant to pregnant women and publish this in the form of an extensive table.

What risk factors were identified?

Age was found to be a major risk factor, with women aged over 30 being at increased risk of moderate to severe COVID-19 outcome. Pregnant healthcare workers were also found to be at higher risk compared with non-healthcare workers, while, as expected, those with an increasing number and severity of pre-existing medical conditions were at higher risk. Possessing one of the pre-defined underlying conditions, on average, contributed towards a 25% increase in the risk of developing moderate to severe COVID-19, while possessing two or three was associated with a 52% and 100% increase, respectively.

Some previous studies have identified a relationship between the trimester of pregnancy and COVID-19 risk. In this study, the trimester in which the women contracted SARS-CoV-2 infection appeared to have little bearing on the severity of disease outcome, nor did the health insurance type of the individual.

The difference in risk between ethnic groups appears minimal at first, though becomes apparent upon adjustment for age as a variable, where the “Black, Non-Hispanic” category was found to have a 22% increased risk over the control “White, Non-Hispanic” group. This could be due to the average age of the former group being lower at the time of pregnancy.

The associations between risk and age, occupation, underlying medical conditions, and ethnicity noted in this study are in-line with findings in the wider literature for non-pregnant women. Each has previously been associated with poorer COVID-19 outcome. Unlike other studies, however, women in the “Hispanic or Latina” category did not have a notably higher risk, even when accounting for age. These women represented almost half of the participants and half of moderate to severe COVID-19 outcomes. This was a ratio that was representative of the region in which the study was undertaken, though is not nationally representative.

Additionally, the group addresses the abundance of women in the study in the second or third trimester compared with those in the first, making identification of trimester-associated risks difficult. The group notes that misclassification of illness severity may have corrupted some of the captured data and that thorough data regarding demographic characteristics is difficult to collect in a critical pandemic situation.

However, the study included a large number of women, and valuable conclusions regarding pregnancy-associated risks may be drawn. Of the underlying medical conditions examined, type 1 or 2 diabetes and cardiovascular disease were both associated with a 54% increase in risk, chronic lung disease with 39%, and obesity with a 32% rise – all of which tend to rise further from this average with age. Those over 35 years of age had a 44% increase in risk compared with those under 20, while women between 30 and 34 years old had a 35% increase, and women aged 20-24 or 25-29 had an increase of 9 or 19%, respectively.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Michael Greenwood

Michael graduated from Manchester Metropolitan University with a B.Sc. in Chemistry in 2014, where he majored in organic, inorganic, physical and analytical chemistry. He is currently completing a Ph.D. on the design and production of gold nanoparticles able to act as multimodal anticancer agents, being both drug delivery platforms and radiation dose enhancers.