Transbaikal is a mountainous region to the east of Lake Baikal in Russia. In October 2009 it was one of the first regions in the Russian Federation to be hit by the H1N1 influenza virus pandemic, which persisted in the region for 12 weeks. According to the official epidemiological data, from a population of 1 117 308 people, 128 463 (11.5%) were infected with the H1N1 influenza virus.The maximum daily morbidity growth rate was 67% in adults and 111.4% in pregnant women. Pregnant women are at an increased risk for flu and its complications and the rate of hospital admissions among pregnant women is higher than for the general population [1][2][3][4]. During the pandemic there were 8570 pregnant women in the region, and 2394 developed the H1N1 virus infection. The incidence of viral pneumonia during pregnancy was 2.47-times higher than in the general population. During the pandemic, 3 pregnant women died. According to the regional epidemiological annual report, the mortality rate was 0.12% in pregnant women compared with 0.05% in the general population.A cross-sectional analysis was performed using the medical histories of 320 pregnant women from the regional hospital in Chita: 220 patients with H1N1 virus infection and 100 pregnant women from the region who did not develop flu. The virus was detected in respiratory specimens from 217 patients using polymerase chain reaction and by virus isolation in cell cultures from the 3 deceased patients.Most patients (n = 203; 92.4%) developed influenza symptoms in the second and third trimester of pregnancy. Of these, 101 (49.8%) women developed pneumonia and 102 (50.2%) women developed an uncomplicated infection.The largest proportion of pregnant women infected by the virus smoked, had an initial body mass index of greater than 25, reported chronic bronchitis, and had unstable arterial pressure. Moreover, a higher percentage of these women reported a history of sexually transmitted infections (i.e. herpes simplex, hepatitis B, chlamydia, mycoplasma, and ureaplasma infections) (Table 1).Nonspecific influenza virus infection preventive actions, according to CDC recommendations [1,2], had been followed by 47 (39.2%) pregnant women with complicated and 42 (42%) pregnant women with uncomplicated influenza virus infection. These figures were much lower than for the group of pregnant women who did not develop the infection (81%; P b 0.01). None of the pregnant women had been vaccinated for seasonal influenza.The 3 pregnant women that died were obese and were smokers. These women had not followed any recommendations concerning the prevention of influenza infection. They sought medical care late and were admitted to hospital in severe respiratory distress.