Despite the fact that influenza vaccination of pregnant women is amply recommended, coverage of influenza vaccination is low. In general, there are few studies on safety of the vaccine to this group, particularly during the first three months of pregnancy or evaluating trivalent vaccines containing inactivated pandemic 2009 H1N1 virus. Studies are controversial regarding passage of maternal antibodies and protection to the newborn. The investigators propose to evaluate safety and immunogenicity of 2011-2012 seasonal trivalent influenza vaccine (Northern hemisphere)(containing an A/California/7/2009 (H1N1)-like virus; an A/Perth/16/2009 (H3N2)-like virus; a B/Brisbane/60/2008-like virus) produced by Sanofi Pasteur. Study design is a Phase II/III, two arm, non-randomized clinical trial. The investigators will recruit 120 pregnant women, 18 to 39 years of age, 14 to 34 week pregnant and 120 non-pregnant women. Trivalent influenza vaccine (0.5ml) will be administered IM in the deltoid zone. Participants will be observed for 30 min post-vaccination for acute adverse reactions and periodically during the 60 days post-vaccination for reactogenicity, adverse effects and severe adverse effects. Baseline and 28 day influenza antibodies will be measured by hemagglutination and microneutralization. Umbilical cord blood (10ml) will be drawn during delivery. Newborns will be followed monthly for growth and morbidity up to six months of age. If necessary, they will be referred for appropriate clinical care. Main outcome will be seroconversion and seroresponse at 28 days post vaccination. Results will be adjusted by study group and other relevant covariables.Safety will be analyzed according to type, severity and study group.