Low despite low vaccine coverage (36.5 ): only one woman had PCR-confirmed A/H1N1 influenza and 10 non-vaccinated women seroconverted between order ITI-007 inclusion and delivery; no serious case of influenza and no hospitalization for influenza were reported. Of note, the low level of influenza infection (rate of 2.6 per 100 pregnant women) is reliable since both PCR and serological data were combined for diagnosis. It could be suggested that the low rate of influenza infection in our cohort was related to the willingness of women to participate to the study with a selection of women understanding 25033180 preventive measures to avoid flu infection. However, vaccination rate (36.5 ), although rather low, was close to the coverage rate in generalPandemic Influenza 2009 Vaccine and PregnancyTable 2. Humoral immunity against pandemic A/H1N1 2009 influenza in vaccinated and non-vaccinated pregnant women at baseline and delivery (n = 678).2009 
A/H1N1 influenza vaccinated pregnant women N = 256 At inclusion Geometric mean titer [95 CI] Number ( ) of women with HI titers .1:40 [95 CI] At delivery Geometric mean titer [95 CI] Number ( ) of women with HI titers .1:40 [95 CI] Seroconversion rate1, Number ( ) of women [95 CI] 49.8 [43.0?7.7] 179 (69.9) [63.9?5.5] 171 (66.8) [60.1?2.5] 7.3 [6.7?.0] 13 (5.1) [2.7?.5]Non-vaccinated pregnant women N =6.7 [6.3?.1] 19 (4.5) [2.7?.0]7.3 [6.8?.8] 26 (6.2) [4.1?.9] 10 (2.3) [1.0?.0]1 Seroconversion rate is given as the percentage of women with a HI titer ,1:10 at inclusion and a titer of 1:40 or greater at delivery, or showing a significant increase in antibody titer defined as a titer of 1:10 or greater at inclusion and at least a fourfold increase in titers between inclusion and delivery. doi:10.1371/journal.pone.0052303.ML 240 chemical information tTable 3. Consequences 
of pandemic A/H1N1 2009 influenza vaccination on pregnancy outcomes.A/H1N1 2009 influenza vaccinated pregnant women n = 320 Gestational age (weeks) at delivery,edian (IQR) Delivery ,37 weeks, n ( ) Onset of labour, n ( ) Spontaneous Induction Caesarean Fever during labour, n ( ) Mode of delivery, n ( ) Spontaneous vaginal delivery Instrumental vaginal delivery Caesarean section Delivery hemorrhage, n ( ) None ,1 liter .1 liter Birth weight, g Mean ,2500, n ( ) [2500?000[, n ( ) 4000, n ( ) Apgar score ,7 at 5 min, n ( ) Infants outcome Alive 23727046 at birth Dead before labour Dead during labour Transfer to neonatal intensive care unit{ Pregnancy loss Fetal malformation Pre eclampsia Fisher’s exact test; First infant for multiple birth. doi:10.1371/journal.pone.0052303.t{ {Non-vaccinated pregnant women n = 557 39.4 (38.7?0.6) 41 (7.4)p-value39.5 (38.6?0.9) 22 (6.9)0.210 (66.7) 71 (22.5) 34 (10.8) 26 (8.1)367 (66.4) 130 (23.5) 56 (10.1) 53 (9.5) 0.51 0.210 (66.7) 34 (10.8) 71 (22.5)379 (68.3) 47 (8.5) 129 (23.2) 0.239 (90.5) 23 (8.7) 2 (0.8)432 (90.9) 35 (7.4) 8 (1.7) -3296.1 22 (6.9) 273 (85.9) 23 (7.2) 1 (0.3)3282.0 33 (6.0) 485 (87.2) 38 (6.8) 5 (0.9) 0.42{ 0.317 (99.7) 1 (0.3) 0 (0.0) 31 (9.8) 1 (0.3) 4 (1.25) 1 (0.3)552 (99.3) 3 (0.5) 1 (0.2) 61 (11.1) 3 (0.5) 3 (0.5) 2 (0.3) 0.58 0.24 0.26 1 -Pandemic Influenza 2009 Vaccine and Pregnancypopulation of French pregnant women (29.3 ) [21] and we showed previously that vaccine coverage was not higher in women with higher risk of exposure to the virus [20]. Other effective ways to reduce the transmission of influenza virus including hygiene habits could have play some role in this cohort population aware of the issues related to A/H1N1 in.Low despite low vaccine coverage (36.5 ): only one woman had PCR-confirmed A/H1N1 influenza and 10 non-vaccinated women seroconverted between inclusion and delivery; no serious case of influenza and no hospitalization for influenza were reported. Of note, the low level of influenza infection (rate of 2.6 per 100 pregnant women) is reliable since both PCR and serological data were combined for diagnosis. It could be suggested that the low rate of influenza infection in our cohort was related to the willingness of women to participate to the study with a selection of women understanding 25033180 preventive measures to avoid flu infection. However, vaccination rate (36.5 ), although rather low, was close to the coverage rate in generalPandemic Influenza 2009 Vaccine and PregnancyTable 2. Humoral immunity against pandemic A/H1N1 2009 influenza in vaccinated and non-vaccinated pregnant women at baseline and delivery (n = 678).2009 A/H1N1 influenza vaccinated pregnant women N = 256 At inclusion Geometric mean titer [95 CI] Number ( ) of women with HI titers .1:40 [95 CI] At delivery Geometric mean titer [95 CI] Number ( ) of women with HI titers .1:40 [95 CI] Seroconversion rate1, Number ( ) of women [95 CI] 49.8 [43.0?7.7] 179 (69.9) [63.9?5.5] 171 (66.8) [60.1?2.5] 7.3 [6.7?.0] 13 (5.1) [2.7?.5]Non-vaccinated pregnant women N =6.7 [6.3?.1] 19 (4.5) [2.7?.0]7.3 [6.8?.8] 26 (6.2) [4.1?.9] 10 (2.3) [1.0?.0]1 Seroconversion rate is given as the percentage of women with a HI titer ,1:10 at inclusion and a titer of 1:40 or greater at delivery, or showing a significant increase in antibody titer defined as a titer of 1:10 or greater at inclusion and at least a fourfold increase in titers between inclusion and delivery. doi:10.1371/journal.pone.0052303.tTable 3. Consequences of pandemic A/H1N1 2009 influenza vaccination on pregnancy outcomes.A/H1N1 2009 influenza vaccinated pregnant women n = 320 Gestational age (weeks) at delivery,edian (IQR) Delivery ,37 weeks, n ( ) Onset of labour, n ( ) Spontaneous Induction Caesarean Fever during labour, n ( ) Mode of delivery, n ( ) Spontaneous vaginal delivery Instrumental vaginal delivery Caesarean section Delivery hemorrhage, n ( ) None ,1 liter .1 liter Birth weight, g Mean ,2500, n ( ) [2500?000[, n ( ) 4000, n ( ) Apgar score ,7 at 5 min, n ( ) Infants outcome Alive 23727046 at birth Dead before labour Dead during labour Transfer to neonatal intensive care unit{ Pregnancy loss Fetal malformation Pre eclampsia Fisher’s exact test; First infant for multiple birth. doi:10.1371/journal.pone.0052303.t{ {Non-vaccinated pregnant women n = 557 39.4 (38.7?0.6) 41 (7.4)p-value39.5 (38.6?0.9) 22 (6.9)0.210 (66.7) 71 (22.5) 34 (10.8) 26 (8.1)367 (66.4) 130 (23.5) 56 (10.1) 53 (9.5) 0.51 0.210 (66.7) 34 (10.8) 71 (22.5)379 (68.3) 47 (8.5) 129 (23.2) 0.239 (90.5) 23 (8.7) 2 (0.8)432 (90.9) 35 (7.4) 8 (1.7) -3296.1 22 (6.9) 273 (85.9) 23 (7.2) 1 (0.3)3282.0 33 (6.0) 485 (87.2) 38 (6.8) 5 (0.9) 0.42{ 0.317 (99.7) 1 (0.3) 0 (0.0) 31 (9.8) 1 (0.3) 4 (1.25) 1 (0.3)552 (99.3) 3 (0.5) 1 (0.2) 61 (11.1) 3 (0.5) 3 (0.5) 2 (0.3) 0.58 0.24 0.26 1 -Pandemic Influenza 2009 Vaccine and Pregnancypopulation of French pregnant women (29.3 ) [21] and we showed previously that vaccine coverage was not higher in women with higher risk of exposure to the virus [20]. Other effective ways to reduce the transmission of influenza virus including hygiene habits could have play some role in this cohort population aware of the issues related to A/H1N1 in.