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. 2016 Jun 6;124(1):48–59. doi: 10.1111/1471-0528.14143

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© 2016 World Health Organization; licensed by John Wiley & Sons Ltd on behalf of Royal College of Obstetricians and Gynaecologists.

This is an open access article distributed under the terms of the Creative Commons Attribution IGO License which permits unrestricted use, distribution and reproduction in any medium, provided that the original work is properly cited.

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Forest plot of individual study results for association between influenza illness during pregnancy and preterm birth. Small, black diamond markers indicate individual study point estimate, with corresponding 95% confidence intervals (CIs) represented by horizontal bars. ^aRisk of preterm birth per 100 women classified as having (exposed) or not having (unexposed) influenza illness/infection during pregnancy. ^bFor observational studies, ‘’ indicates a Newcastle‐Ottawa Score ≥8, risk of diagnostic ascertainment bias not rated as ‘very high’, and exposure not measured using self‐reported questionnaire. ^cCrude estimates were used in place of adjusted estimates when the latter were not provided. ^dHansen (2012)40 is shown twice: one estimate for 2009 A (pH1N1) and one for 2008–2009 influenza season. ^eHåberg (2013)39 did not provide the risk of preterm birth by exposure group. Overall risk in the study population was 5.4/100 singleton live births. ^fMorken (2011)41 studied spontaneous preterm birth only. ^gBaseline risk of preterm birth in the study population was not provided.44

Inline graphic — Forest plot of individual study results for association between influenza illness during pregnancy and preterm birth. Small, black diamond markers indicate individual study point estimate, with corresponding 95% confidence intervals (CIs) represented by horizontal bars. ^aRisk of preterm birth per 100 women classified as having (exposed) or not having (unexposed) influenza illness/infection during pregnancy. ^bFor observational studies, ‘’ indicates a Newcastle‐Ottawa Score ≥8, risk of diagnostic ascertainment bias not rated as ‘very high’, and exposure not measured using self‐reported questionnaire. ^cCrude estimates were used in place of adjusted estimates when the latter were not provided. ^dHansen (2012)40 is shown twice: one estimate for 2009 A (pH1N1) and one for 2008–2009 influenza season. ^eHåberg (2013)39 did not provide the risk of preterm birth by exposure group. Overall risk in the study population was 5.4/100 singleton live births. ^fMorken (2011)41 studied spontaneous preterm birth only. ^gBaseline risk of preterm birth in the study population was not provided.44