Pregnant Women Make Up High Rate of Hospitalized Flu Patients

January 7, 2022
Kevin Kunzmann

Cross-sectional data from the last decade of flu seasons show pregnant women are infrequently vaccinated and at greater risk of severe disease.

Nearly one-third of all reproductive-age women hospitalized with influenza in the last decade were pregnant during their admission, according to data from a new cross-sectional study.

In new data from an assessment of US flu seasons from 2010-11 to 2018-19, a team of investigators from the Centers for Disease Control & Prevention (CDC) reported pregnancy is notably prevalent among young women hospitalized with influenza. What’s more, a majority of pregnant patients hospitalized with flu since 2010-11 were in their third trimester.

Led by Rachel A. Holstein, MPH, of the Influenza Division at the CDC’s National Center for Immunization and Respiratory Diseases, investigators sought to describe the clinical and demographic characteristics of hospitalized pregnant women with the flu. The repeated cross-sectional study, funded by the CDC, also observed the clinical outcomes of such high-risk patients.

Indeed, Holstein and colleagues noted that pregnant women may be at an increased risk of severe outcomes associated with influenza. Their observed population included pregnant women aged 15-44 years old hospitalized with laboratory-confirmed flu.

Data were collected from the population-based US Influenza Hospitalization Surveillance Network to represent the 9 observed flu seasons. Patients’ clinical characteristics, their care, and in-hospital maternal and fetal outcomes were assessed via medical chart abstraction. Holstein and colleagues conducted multivariable logistic regression analyses to evaluate the link between influenza A subtype and severe maternal influenza-associated outcomes including intensive care unit (ICU) admission, mechanical ventilation use, extracorporeal membrane oxygenation, or in-hospital death.

The assessment included 9652 reproductive-aged women hospitalized with influenza between 2010-19; among them, 2690 (27.9%) were pregnant. Median pregnant patient age was 28 years old, with nearly two-thirds (62%) being in their first trimester and nearly half (42%) having ≥1 underlying condition.

Only 32% of women hospitalized with influenza were vaccinated against it; 88% received antiviral therapy while in hospital care. ICU admission (5%), mechanical ventilation (2%), and death (0.3% [n = 8]) were rare outcomes among observed women.

However, pregnant women hospitalized with influenza A H1N1 were nearly twice more likely than those who were not pregnant to have a severe disease outcome (adjusted RR, 1.9; 95% CI, 1.3 - 2.8). Approximately three-fourths (71%) of women were still pregnant during hospital discharge; 96% of the 754 women who were no longer pregnant at discharge had a live birth, and 3% experienced fetal loss.

Despite investigators being limited in post-discharge data for patients, the team concluded the findings elicit concern over the protection of pregnant women against influenza.

“Over 9 influenza seasons, one third of reproductive-aged women hospitalized with influenza were pregnant,” they wrote. “Influenza A H1N1 was associated with more severe maternal outcomes. Pregnant women remain a high-priority target group for vaccination.”

The study, “Characteristics and Outcomes of Hospitalized Pregnant Women With Influenza, 2010 to 2019,” was published online in Annals of Internal Medicine.


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