Influenza Complicating Delivery Hospitalization and Its Association With Severe Maternal Morbidity in the United States, 2000–2018

OBJECTIVE To characterize trends of an influenza diagnosis at delivery hospitalization and its association with severe maternal morbidity. METHODS We conducted a repeated cross-sectional analysis of delivery hospitalizations using the Nationwide Inpatient Sample from 2000 to 2018. We assessed the association between an influenza diagnosis at delivery hospitalization and severe maternal morbidity excluding transfusion per Centers for Disease Control and Prevention criteria. Secondary outcomes included maternal death and morbidity measures associated with influenza (mechanical intubation and ventilation, sepsis and shock, and acute respiratory distress syndrome [ARDS]) and obstetric complications (preterm birth and hypertensive disorders of pregnancy). We assessed trends of severe maternal morbidity by annual influenza season and the association between influenza and severe maternal morbidity using multivariable log-linear regression, adjusting for demographic, clinical, and hospital characteristics. RESULTS Of 74.7 million delivery hospitalizations, 23 per 10,000 were complicated by an influenza diagnosis. The rate of severe maternal morbidity was higher with an influenza diagnosis compared with those without influenza (86-410 cases vs 53-70 cases/10,000 delivery hospitalizations). Women with an influenza diagnosis at delivery hospitalization were at an increased risk of severe maternal morbidity compared with those without influenza (2.3 vs 0.7%; adjusted risk ratio 2.24, 95% CI 2.17-2.31). This association held for maternal death, mechanical intubation, sepsis and shock, and ARDS-as well as obstetric complications, including preterm birth and hypertensive disorders of pregnancy. CONCLUSION Pregnant women with influenza are at increased risk of severe maternal morbidity, as well as influenza-related maternal and obstetric complications. These results emphasize the importance of primary prevention and recognition of influenza infection during pregnancy to reduce downstream maternal morbidity and mortality.