title: Seasonal influenza vaccination during pregnancy and the risks of preterm delivery and small for gestational age birth.
abstract: BACKGROUND
  Influenza vaccination is routinely recommended for pregnant women, yet information on perinatal outcomes is sparse.
  
  
  METHODS
  We investigated the associations between trivalent (seasonal) influenza vaccination during pregnancy and the risks of preterm delivery (PTD, live birth <37 weeks gestation) and small for gestational age birth (SGA, <10th percentile in weight for sex-specific gestational age) during the influenza seasons 2006-07 through 2009-10. The study population included 1619 mothers of live-born, non-malformed singleton infants interviewed as part of the Slone Epidemiology Center's Birth Defects Study. Associations between influenza vaccination and PTD and SGA were assessed using Cox and logistic regression models, respectively, with propensity scores used to adjust for confounding. Women vaccinated against pandemic H1N1 were excluded from the analysis.
  
  
  RESULTS
  Influenza vaccination during pregnancy showed a near null association with PTD for influenza seasons 2006-07 through 2008-09 compared with unvaccinated women [adjusted hazard ratios (aHR) ranged from 0.79 [95% confidence interval (CI) 0.28, 2.21] in 2007-08 to 1.08 [95% CI: 0.40, 2.95] in 2008-09]. For 2009-10, the risk of PTD was higher in vaccinated women (aHR, 7.81 [95% CI: 2.66, 23.0]). Influenza vaccination was not associated with appreciable risks for SGA for all seasons with sufficient numbers of exposed SGA.
  
  
  CONCLUSIONS
  Though limited by study size, these findings add support to previous observations of little or no increased risk of PTD or SGA associated with seasonal influenza vaccination for three of the four influenza seasons in our study. The increased risk of PTD observed for the 2009-10 influenza season warrants further investigation.
authors.affiliation: Slone Epidemiology Center, Boston University, Boston, MA; Epidemiology Department, School of Public Health, Boston University, Boston, MA.
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Ahrens
authors.forename: Carol
authors.initials: C
authors.lastname: Louik
authors.forename: Stephen
authors.initials: S
authors.lastname: Kerr
authors.forename: Allen A
authors.initials: AA
authors.lastname: Mitchell
authors.forename: Martha M
authors.initials: MM
authors.lastname: Werler
mesh_terms: D000328:Adult; D000013:Congenital Abnormalities / Q000453:epidemiology* / Q000209:etiology; D062665:Epidemiological Monitoring; D005260:Female; D005865:Gestational Age; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age; D053118:Influenza A Virus, H1N1 Subtype / Q000472:pathogenicity; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000009:adverse effects*; D007251:Influenza, Human / Q000150:complications / Q000453:epidemiology / Q000517:prevention & control*; D008297:Male; D011159:Population Surveillance; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious / Q000453:epidemiology* / Q000276:immunology / Q000517:prevention & control; D047928:Premature Birth / Q000139:chemically induced / Q000453:epidemiology*; D015995:Prevalence; D018570:Risk Assessment; D012307:Risk Factors; D012621:Seasons; D014481:United States / Q000453:epidemiology; D014611:Vaccination / Q000009:adverse effects
chemical_list: D007252:Influenza Vaccines
keywords: infant; influenza; pregnancy; preterm birth; small for gestational age; vaccination