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Perinatal outcomes after maternal 2009/H1N1 infection: national cohort study

BMJ 2011; 342 doi: (Published 14 June 2011) Cite this as: BMJ 2011;342:d3214
  1. Matthias Pierce, medical statistician1,
  2. Jennifer J Kurinczuk, reader in perinatal epidemiology and deputy director1,
  3. Patsy Spark, programmer1,
  4. Peter Brocklehurst, clinical epidemiologist and director1,
  5. Marian Knight, senior clinical research fellow1
  6. on behalf of UKOSS
  1. 1National Perinatal Epidemiology Unit, University of Oxford, Oxford OX3 7LF, UK
  1. Correspondence to: M Knight marian.knight{at}
  • Accepted 13 April 2011


Objectives To follow up a UK national cohort of women admitted to hospital with confirmed 2009/H1N1 influenza in pregnancy in order to obtain a complete picture of pregnancy outcomes and estimate the risks of adverse fetal and infant outcomes.

Design National cohort study.

Setting 221 hospitals with obstetrician led maternity units in the UK.

Participants 256 women admitted to hospital with confirmed 2009/H1N1 in pregnancy during the second wave of pandemic infection between September 2009 and January 2010; 1220 pregnant women for comparison.

Main outcome measures Rates of stillbirth, perinatal mortality, and neonatal mortality; odds ratios for infected versus comparison women.

Results Perinatal mortality was higher in infants born to infected women (10 deaths among 256 infants; rate 39 (95% confidence interval 19 to 71) per 1000 total births) than in infants of uninfected women (9 deaths among 1233 infants; rate 7 (3 to 13) per 1000 total births) (P<0.001). This was principally explained by an increase in the rate of stillbirth (27 per 1000 total births v 6 per 1000 total births; P=0.001). Infants of infected women were also more likely to be born prematurely than were infants of comparison women (adjusted odds ratio 4.0, 95% confidence interval 2.7 to 5.9). Infected women who delivered preterm were more likely to be infected in their third trimester (P=0.046), to have been admitted to an intensive care unit (P<0.001), and to have a secondary pneumonia (P=0.001) than were those who delivered at term.

Conclusions This study suggests an increase in the risk of poor outcomes of pregnancy in women infected with 2009/H1N1, which reinforces the message from studies of maternal risk alone. The health of pregnant women is an important public health priority in future waves of this and other influenza pandemics.


  • This study would not have been possible without the contribution and enthusiasm of the UKOSS reporting clinicians who notified cases and completed the data collection forms.

  • Contributors: MP assisted with coding of data, did the analysis, and wrote the first draft of the paper. JJK provided advice at every stage of the study and contributed to the writing and editing of the paper. PS assisted with coding of data, validated the data, and contributed to writing and editing the paper. PB provided advice at every stage of the study and contributed to the writing and editing of the paper. MK designed the study, coordinated data collection, coded data, supervised the analysis, and contributed to the writing and editing of the paper. All authors had full access to all of the data (including statistical reports and tables) in the study and can take responsibility for the integrity of the data and the accuracy of the data analysis. MK is the guarantor.

  • Funding: The research presented here was funded by a grant from the National Institute for Health Research Health Technology Assessment Programme, grant reference 09/84/47. MK was funded by a personal award from the NIHR National Coordinating Centre for Research Capacity Development. All researchers are independent of the funders.

  • Competing interests: All authors have completed the Unified Competing Interest form at (available on request from the corresponding author) and declare that none have support from any company for the submitted work; they have had no relationships with companies that might have an interest in the submitted work in the previous three years; and they have no non-financial interests that may be relevant to the submitted work.

  • Ethical approval: This study was approved by the County Durham and Tees Valley 1 Research Ethics Committee (study reference 09/H0905/66).

  • Data sharing: Data sharing is governed by the National Perinatal Epidemiology Unit data sharing policy, which may be obtained from the corresponding author at marian.knight{at}

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