Pregnant and recently postpartum women with influenza are more likely to develop severe illness and die than the general population, based on data from seasonal influenza and from the influenza pandemics of 1918 to 1919, 1957 to 1958, and 2009 to 2010. The increased severity of influenza in pregnant and recently postpartum women is thought to be related to normal physiologic changes that occur during pregnancy. For example, heart rate and oxygen consumption increase and lung capacity decreases. Because of the increased severity of influenza in pregnancy and the postpartum period, inactivated influenza vaccine is recommended for these women, regardless of trimester of pregnancy. In addition, pregnant and postpartum women with suspected or confirmed influenza should receive prompt empiric treatment with an appropriate antiviral medication.