OBJECTIVE: To evaluate associations between laboratory-confirmed 2009 H1N1 
influenza infection and obstetric and neonatal outcomes.
STUDY DESIGN: A multicenter cohort study was performed comparing 
laboratory-confirmed cases of 2009 H1N1 infection during pregnancy (N=142) with 
matched controls (N=710). Subanalysis was also performed comparing severely 
infected (hospitalized) women with controls.
RESULT: No outcome differences were noted in comparing all women with H1N1 with 
controls. Women with severe infection had a higher incidence of delivering a 
small for gestational age (SGA) infant: 18.8% (6/32) versus 7.4% (52/707), 
adjusted odds ratio 2.35 (95% confidence interval 1.03, 5.36, P=0.02). Mean 
birth weight was 3013.0 g among severely infected women and 3223.3 g in controls 
(P=0.08), and incidence of preterm delivery was 25.0% (8/32) and 11.6% (82/710) 
(P=0.08), respectively.
CONCLUSION: Pregnant women with mild clinical illness secondary to 2009 H1N1 
were not at a greater risk of adverse pregnancy outcomes. However, severely 
infected women were more likely to deliver SGA infants.