39 Influenza in pregnancy and severe maternal morbidity in the United States, 2000-2015


      Women with influenza in pregnancy have historically been shown to be at increased risk of adverse pregnancy outcomes, but contemporary U.S. data are lacking. Our objective was to evaluate the frequency of influenza during pregnancy over time and its association with maternal morbidity and mortality.

      Study Design

      A repeated cross-sectional analysis of pregnant women 15-54 years using the National (Nationwide) Inpatient Sample from 2000 to 2015. The primary outcome included 21 indicators of severe maternal morbidity (SMM) during delivery hospitalization excluding transfusion per Centers for Disease Control and Prevention criteria, as well as individual outcomes associated with influenza morbidity: ventilation/tracheostomy, sepsis/shock, and adult respiratory distress syndrome (ARDS). We analyzed the risk of SMM by annual flu seasons, reporting trends as average annual percent change (AAPC). We determined the association between influenza and maternal morbidity using log-linear regression, adjusting for demographic, hospital, and maternal factors.


      Among 62.6 million deliveries with a SMM rate of 67 per 10,000, the SMM rate was over 3 times higher with versus without influenza (208 versus 66 per 10,000, p<0.01). The risk of SMM increased steadily with an influenza diagnosis compared to those without (AAPC of 5.3% [95% CI: 3.6, 7.1] vs. 2.4% [95% CI: 0.8, 4.0] respectively) [Figure]. Influenza during pregnancy was associated with a two-fold increased risk of SMM (adjusted risk ratio, aRR=2.08, 95% CI: 2.01, 2.15), as well as ventilation/tracheostomy (aRR=6.04, 95% CI: 5.14, 7.09, sepsis/shock (aRR=3.23, 95% CI: 2.80, 3.71), and ARDS (aRR=5.76, 95% CI: 5.37, 6.18) [Table].


      Pregnant women with influenza are at higher risk of SMM, and this risk has increased over time across the U.S. Continued efforts of increasing universal influenza vaccination in pregnancy and identifying which pregnant women with influenza are at the highest risk of adverse outcomes should be a public health priority to improve maternal health and reduce morbidity and mortality.
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