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H1N1v influenza ('swine flu') in pregnancy

Key points

  • Currently we have limited information about the complications of H1N1v infection ('swine flu') in pregnancy in the UK.
  • Experience in other countries and from previous influenza pandemics suggests that pregnant women are more susceptible to complications of infection.
  • Rapid collection and analysis of information is needed in the course of the current pandemic to inform guidance for management.
  • This study will provide national information about women hospitalised with H1N1v in pregnancy and rapid analysis of these data to produce updated monthly guidance for clinicians.

Surveillance Period

September 2009 – February 2010


Influenza infection during pregnancy is associated with adverse maternal and fetal outcomes, including probable increases in the risk of maternal pneumonia and possible increases in risks of certain congenital malformations[1][2][3][4][5][6]. Recent US H1N1 pandemic experience as well as data from previous influenza pandemics indicates higher morbidity and mortality among pregnant women[7][8][9][10]. However, detailed epidemiological studies investigating risks in subgroups of pregnant women and the impact of pregnancy management strategies on outcomes are currently lacking.

This research will identify through UKOSS, all pregnant women hospitalised with confirmed or suspected influenza A/H1N1v in the UK. The study will collect information on their demographic and pregnancy characteristics as well as management, including use and timing of use of antivirals, as well as mode and timing of delivery. In addition, the study will collect data on the incidence of complications of both influenza and pregnancy, and the outcomes for both women and their infants. This information will be used to investigate the relationship between demographic, pregnancy characteristics, management and outcomes in order to generate immediate recommendations for changes in practice to improve outcomes for this vulnerable group.


This study will use a new online reporting system which may be accessed using the following instructions:

  1. Clinicians wishing to report a case should click the link "Report a case of H1N1 influenza" on the UKOSS website ( or go directly to (link decomissioned). Any doctor or midwife in the hospital may report a case.
  2. When you click on the link, you will be asked to select your job title (selected from a list), your name, a personal contact number (in case we need to phone you) and your email address. Select your hospital name from the list, and enter the main telephone number of your hospital (to help provide an identification check).
  3. After submitting these details, you will be registered into the system and an email will be sent to the address you provided, giving you a link to a second page.
  4. Click on this link in your email (or copy and paste it into your web browser) to open the page where you will be asked to re-enter your email (as an additional security check) and click the button "Generate the PDF".
  5. The PDF of the Influenza form with a unique identification number will be shown in your browser window.
  6. Please print and complete the form and post back to the usual address: UKOSS, National Perinatal Epidemiology Unit, University of Oxford, Old Road Campus, Oxford OX3 7LF
  7. To report additional cases in the same session, use your browser's 'Back' button and click the "Generate the PDF" button again to get another form with its own identification number.
  8. Once you have created a case, a confirmation email will be sent to you giving you the identification number of the case.
  9. Keep your registration email, as this contains a code that is unique to you, without which you will not be able to report cases. The next time you wish to report a case, use this link and you will not have to re-enter your personal details.
  10. If you have any problems, please phone the UKOSS team on 01865 289714.

Research Objectives

  1. To determine:
    1. the incidence of hospitalisation with influenza A/H1N1v in pregnancy
    2. the effect of H1N1v Influenza infection and/or treatment with neuraminidase antiviral drugs in pregnant women (timing of use, dose and agent) on pregnancy outcome, including specific adverse or beneficial effects of antiviral treatment on eventual maternal and fetal outcome
    3. the influence of demographic or pregnancy characteristics and additional aspects of pregnancy management on outcomes for mother and infant
  2. To produce guidance on the management of H1N1v infection in pregnancy by monthly review of emerging data from this study such that outcomes for women and infants are optimised during the current pandemic.

Case definition

Any woman admitted to hospital with confirmed or suspected H1N1v influenza infection in pregnancy.


National Institute for Health Research (NIHR)

Ethics committee approval

The study has been approved by the County Durham and Tees Valley 1 REC (study ref 09/H0905/66).


Marian Knight, Jennifer Kurinczuk, Peter Brocklehurst, NPEU

Simon Thomas, Laura Yates, Sally Stephens, UK Teratology Information Service


  1. ^ RLeck I. Incidence of malformations following influenza epidemics. Br J Prev Soc Med 1963;17:70-80.
  2. ^ Busby A, Dolk H, Armstrong B. Eye anomalies: seasonal variation and maternal viral infections. Epidemiology 2005;16(3):317-22.
  3. ^ Doll R, Hill AB, Sakula J. Asian influenza in pregnancy and congenital defects. Br J Prev Soc Med 1960;14:167-72.
  4. ^ Coffey VP, Jessop WJ. Maternal influenza and congenital deformities: a prospective study. Lancet 1959;2(7109):935-8.
  5. ^ Hakosalo J, Saxen L. Influenza epidemic and congenital defects. Lancet 1971;2(7738):1346-7.
  6. ^ Acs N, Banhidy F, Puho E, Czeizel AE. Maternal influenza during pregnancy and risk of congenital abnormalities in offspring. Birth Defects Res A Clin Mol Teratol 2005;73(12):989-96.
  7. ^ Neuzil KM, Reed GW, Mitchel EF, Simonsen L, Griffin MR. Impact of influenza on acute cardiopulmonary hospitalizations in pregnant women. Am J Epidemiol 1998;148(11):1094-102.
  8. ^ Greenberg M, Jacobziner H, Pakter J. Maternal mortality in the epidemic of Asian influenza, New York City, 1957. Am J Obstet Gynecol 1958;76:897-902.
  9. ^ Hospitalized patients with novel influenza A (H1N1) virus infection - California, April-May, 2009. MMWR Morb Mortal Wkly Rep 2009;58(19):536-41.
  10. ^ Novel influenza A (H1N1) virus infections in three pregnant women - United States, April-May 2009. MMWR Morb Mortal Wkly Rep 2009;58(18):497-500.

Updated: Friday, 09 October 2020 10:27 (v6)