A multicenter cohort study of pregnancy outcomes among women with laboratory-confirmed H1N1 influenza

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.