Circulating Influenza Virus and Adverse Pregnancy Outcomes: A Time-Series Study

Am J Epidemiol. 2016 Aug 1;184(3):163-75. doi: 10.1093/aje/kww044. Epub 2016 Jul 22.


Individual-level epidemiologic studies of pregnancy outcomes after maternal influenza are limited in number and quality and have produced inconsistent results. We used a time-series design to investigate whether fluctuation in influenza virus circulation was associated with short-term variation in population-level rates of preterm birth, stillbirth, and perinatal death in Ontario between 2003 and 2012. Using Poisson regression, we assessed the association between weekly levels of circulating influenza virus and counts of outcomes offset by the number of at-risk gestations during 3 gestational exposure windows. The rate of preterm birth was not associated with circulating influenza level in the week preceding birth (adjusted rate ratio = 1.01, 95% confidence interval: 1.00, 1.02) or in any other exposure window. These findings were robust to alternate specifications of the model and adjustment for potential confounding. Stillbirth and perinatal death rates were similarly not associated with gestational exposure to influenza circulation during late pregnancy. We could not assess mortality outcomes relative to early gestational exposure because of missing dates of conception for many stillbirths. In this time-series study, population-level influenza circulation was not associated with short-term variation in rates of preterm birth, stillbirth, or perinatal death.

Keywords: influenza; pregnancy; preterm birth; stillbirth; time-series study.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Birth Certificates
  • Female
  • Humans
  • Infant, Newborn
  • Influenza A Virus, H1N1 Subtype / isolation & purification*
  • Influenza, Human / complications
  • Influenza, Human / epidemiology*
  • Maternal Age
  • Maternal Health / statistics & numerical data
  • Medical Record Linkage
  • Middle Aged
  • Ontario / epidemiology
  • Perinatal Death / etiology
  • Poisson Distribution
  • Population Surveillance / methods
  • Pregnancy
  • Pregnancy Complications, Infectious / epidemiology*
  • Pregnancy Complications, Infectious / virology
  • Pregnancy Outcome / epidemiology*
  • Premature Birth / epidemiology
  • Premature Birth / virology
  • Residence Characteristics / statistics & numerical data
  • Space-Time Clustering
  • Stillbirth / epidemiology
  • Young Adult

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