Abstract

BackgroundAlthough pregnant women are considered at high risk for severe influenza disease, comparative studies of maternal influenza and birth outcomes have not been comprehensively summarised.ObjectiveTo review comparative studies evaluating maternal influenza disease and birth outcomes.Search strategyWe searched bibliographic databases from inception to December 2014.Selection criteriaStudies of preterm birth, small‐for‐gestational‐age (SGA) birth or fetal death, comparing women with and without clinical influenza illness or laboratory‐confirmed influenza infection during pregnancy.Data collection and analysisTwo reviewers independently abstracted data and assessed study quality.Main resultsHeterogeneity across 16 studies reporting preterm birth precluded meta‐analysis. In a subgroup of the highest‐quality studies, two reported significantly increased preterm birth (risk ratios (RR) from 2.4 to 4.0) following severe 2009 pandemic H1N1 (pH1N1) influenza illness, whereas those assessing mild‐to‐moderate pH1N1 or seasonal influenza found no association. Five studies of SGA birth showed no discernible patterns with respect to influenza disease severity (pooled odds ratio 1.24; 95% CI 0.96–1.59). Two fetal death studies were of sufficient quality and size to permit meaningful interpretation. Both reported an increased risk of fetal death following maternal pH1N1 disease (RR 1.9 for mild‐to‐moderate disease and 4.2 for severe disease).ConclusionsComparative studies of preterm birth, SGA birth and fetal death following maternal influenza disease are limited in number and quality. An association between severe pH1N1 disease and preterm birth and fetal death was reported by several studies; however, these limited data do not permit firm conclusions on the magnitude of any association.Tweetable abstractComparative studies are limited in quality but suggest severe pandemic H1N1 influenza increases preterm birth.

Highlights

  • Pregnant women are considered vulnerable to serious influenza disease and related complications

  • Comparative studies of preterm birth, SGA birth and fetal death following maternal influenza disease are limited in number and quality

  • An association between severe pandemic H1N1 (pH1N1) disease and preterm birth and fetal death was reported by several studies; these limited data do not permit firm conclusions on the magnitude of any association

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Summary

Introduction

Pregnant women are considered vulnerable to serious influenza disease and related complications. On the basis of evidence documenting excess influenza-related mortality in pregnant women during historical and recent pandemics[1,2,3] and higher rates of influenza-related morbidity requiring hospitalisation during seasonal epidemics,[4,5,6] many countries advise that women who are, or will be, pregnant during the influenza season be immunised with inactivated influenza vaccine.[7,8,9] Since 2012, the World Health Organization (WHO) has recommended that countries expanding or initiating influenza vaccination programs prioritize pregnant women for vaccine receipt.[10] While the primary goal of these recommendations is to protect pregnant women from severe influenza disease, benefits of maternal immunisation have been shown to extend to neonates through transfer of maternal antibodies, providing passive immunity against influenza virus infection.[11]. Pregnant women are considered at high risk for severe influenza disease, comparative studies of maternal influenza and birth outcomes have not been comprehensively summarised

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