Pregnant women with influenza are more likely to develop severe illness and to die than the general population, based on data from seasonal influenza and from the influenza pandemics of 1918-1919, 1957-1958, and 2009-2010. The increased severity of influenza in pregnancy is believed to be related to physiologic changes in pregnancy. For example, changes to the cardiovascular and respiratory systems result in increased heart rate and oxygen consumption and decreased lung capacity, and immunologic alterations result in a shift away from cell-mediated immunity. Because of the increased severity of influenza in pregnancy, inactivated influenza vaccine is recommended for pregnant women, regardless of trimester of pregnancy. In addition, pregnant women with suspected or confirmed influenza should receive prompt empiric treatment with an appropriate antiviral medication.
CLINICAL COURSE IN PREGNANCY
Pregnant women are more severely affected by influenza compared with the general population:
●During the 1918-1919 and 1957-1958 pandemics, pregnant women had high mortality rates [1-4].
●During the 2009 H1N1 pandemic, a disproportionate number of deaths occurred among pregnant women, with pregnant women accounting for 5 percent of all deaths, even though pregnant women account for only 1 percent of the United States general population . Pregnant women were also more likely to be hospitalized during the 2009 H1N1 pandemic than the general population ; large case series of critically ill pregnant patients were reported from the US [5,7,8] and other countries [9-12]. Although pregnant women were more severely affected once infected, there was no evidence that pregnant women were more susceptible to infection with 2009 H1N1 influenza virus .
●Pregnant women have increased rates of hospitalization for acute respiratory disease during influenza seasons compared to nonpregnant women, which supports increased severity of seasonal influenza during pregnancy [14,15]. However, due to low rates of diagnostic testing, studies with confirmed cases of seasonal influenza comparing pregnant and nonpregnant women are lacking.