Pregnant women represent a disproportionately higher percentage of severe cases with the increased risk ranging from four-to 10-fold greater compared with the general population ( Figure 2 ). Increased morbidity and mortality in pregnant women has been reported in many datasets [5, 14, 27, 28, 36, 37, 41, [43] [44] [45] . The disease course and clinical presentation [46] [47] [48] has been studied and comparisons of disease in pregnant women to age-matched non-pregnant women [37, 49, 50] or to the general population [51] have been made. Disease severity is increased during the second and third trimester. However, no clear clinical parameter has been associated with pregnancy-associated increased morbidity and mortality. There are no significant differences in the general symptoms of disease, the progression to viral pneumonia, acute respiratory distress syndrome (ARDS) or secondary bacterial pneumonia in pregnant women compared to the control populations. Severe disease was also associated with a greater than sixfold increase in adverse neonatal outcomes when compared with pregnant women suffering mild disease [49] . An increased risk of severe disease may be present during the early postpartum period but the reported number of cases is limited and requires additional investigation [37, 50] . Female to male ratios of hospitalization with confirmed 2009 H1N1 were calculated using published datasets [5, 6, 14, 16, [27] [28] [29] [30] [32] [33] [34] [35] [36] [37] 43, [134] [135] [136] . Pink bars = higher rates of hospitalization in females; blue bars = higher rates of hospitalization in males; grey bars = similar hospitalization rates in males and females. Details about sample sizes, time of data collection, and criteria for hospitalization are contained within each individual reference.