Associations of influenza, chronic comorbid conditions, and severe maternal morbidity among pregnant women in the United States with influenza at delivery hospitalization, 2000-2015.

BACKGROUND

Chronic comorbid conditions increase the risk of influenza-related morbidity. Whether this holds for pregnant women who are at a high risk of complications from influenza remains to be determined.

OBJECTIVE

This study aimed to determine whether chronic comorbid conditions are associated with an increased risk of severe maternal morbidity among pregnant women with an influenza diagnosis at delivery hospitalization.

STUDY DESIGN

We performed a cross-sectional analysis of delivery hospitalizations complicated by an influenza diagnosis using the National Inpatient Sample from 2000 to 2015. We assessed 4 prevalent chronic comorbid conditions associated with increased influenza complications outside of pregnancy, obstructive lung disease (asthma and chronic obstructive pulmonary disease), chronic hypertension, obesity, and pregestational diabetes mellitus, overall and individually. The primary outcome was severe maternal morbidity, excluding transfusion as defined by the Centers for Disease Control and Prevention, and the secondary outcomes were specific severe maternal morbidity measures that were recognized as influenza-related complications, acute respiratory distress syndrome, mechanical intubation and ventilation, and sepsis and shock. Multivariable survey-weighted log-linear models were used, adjusting for patient, hospital, and clinical characteristics.

RESULTS

Of 62.7 million delivery hospitalizations, 144,572 (0.2%) were complicated by an influenza diagnosis at delivery hospitalization (23 cases of influenza per 10,000 delivery hospitalizations) and 36,054 (24.9%) with ≥1 chronic comorbid conditions, of which 77.4% included obstructive lung disease. Pregnant women with an influenza diagnosis at delivery hospitalization with chronic comorbid conditions had a slightly higher risk of severe maternal morbidity than those without (2.6% vs 1.7%; adjusted risk ratio, 1.11; 95% confidence interval, 1.03-1.21) and acute respiratory distress syndrome (0.9% vs 0.5%; adjusted risk ratio, 1.42; 95% confidence interval, 1.23-1.64) and mechanical intubation and ventilation (0.2% vs 0.1%; adjusted risk ratio, 1.92; 95% confidence interval, 1.37-2.69) but a lower risk of sepsis and shock (0.2% vs 0.3%; adjusted risk ratio, 0.57; 95% confidence interval, 0.45-0.73). Regarding specific conditions, obstructive lung disease was associated with an increased risk of severe maternal morbidity (adjusted risk ratio, 1.21; 95% confidence interval, 1.11-1.32) and acute respiratory distress syndrome (adjusted risk ratio, 1.54; 95% confidence interval, 1.32-1.79) and mechanical intubation and ventilation (adjusted risk ratio, 2.80; 95% confidence interval, 2.00-3.91). Chronic hypertension was associated with an increased risk of acute respiratory distress syndrome (adjusted risk ratio, 1.70; 95% confidence interval, 1.16-2.49) but a lower risk of sepsis and shock (adjusted risk ratio, 0.34; 95% confidence interval, 0.13-0.85). Obesity was associated with a lower risk of severe maternal morbidity (adjusted risk ratio, 0.84; 95% confidence interval, 0.74-0.97). Pregestational diabetes mellitus was not associated with severe maternal morbidity.

CONCLUSION

Among women with a diagnosis of influenza at delivery hospitalization, chronic comorbid conditions may increase the risk of severe maternal morbidity and particularly outcomes related to influenza. These results can inform efforts to increase influenza vaccination for all pregnant women, in particular those with chronic comorbidities.