We report the immunogenicity of trivalent influenza immunization in 29 pregnant compared to 22 non-pregnant women. We obtained blood on day 0 prior to 2011-2012 influenza vaccine administration, and day 28 post-immunization. Hemagglutination inhibition (HAI) geometric mean titers were similar before immunization but were significantly reduced by 40% to 50% in pregnant women post-immunization for A/California (H1N1) (p=0.027) and A/Perth (H3N2) (p=0.037). Post-immunization HAI titers were similar between groups for B/Brisbane (p=0.390). The geometric mean ratio (fold rise) for H1N1 was non-significantly reduced in pregnant participants (p=0.089). The percent of participants who seroconverted and achieved seroprotection were similar between groups.