title: Vaccination against pandemic A/H1N1 2009 influenza in pregnancy and risk of fetal death: cohort study in Denmark.
abstract: OBJECTIVE
  To investigate whether an adjuvanted pandemic A/H1N1 2009 influenza vaccine in pregnancy was associated with an increased risk of fetal death.
  
  
  METHODS
  Nationwide register based cohort study.
  
  
  METHODS
  Denmark.
  
  
  METHODS
  All clinically recognised singleton pregnancies that ended between November 2009 and September 2010. Individual level data on exposure to an inactivated AS03 pandemic A/H1N1 2009 influenza vaccine (Pandemrix) and potential confounders were linked to the study cohort using a unique person identifier.
  
  
  METHODS
  The primary outcome measure was risk of fetal death (spontaneous abortion and stillbirth combined) in H1N1 vaccinated compared with unvaccinated pregnancies, adjusting for propensity scores. Secondary outcome measures were spontaneous abortion (between seven and 22 weeks' gestation) and stillbirth (after 22 completed weeks' gestation).
  
  
  RESULTS
  The cohort comprised 54,585 pregnancies; 7062 (12.9%) women were vaccinated against pandemic A/H1N1 2009 influenza during pregnancy. Overall, 1818 fetal deaths occurred (1678 spontaneous abortions and 140 stillbirths). Exposure to the H1N1 vaccine was not associated with an increased risk of fetal death (adjusted hazard ratio 0.79, 95% confidence interval 0.53 to 1.16), or the secondary outcomes of spontaneous abortion (1.11, 0.71 to 1.73) and stillbirth (0.44, 0.20 to 0.94). Estimates for fetal death were similar in pregnant women with (0.82, 0.44 to 1.53) and without comorbidities (0.77, 0.47 to 1.25).
  
  
  CONCLUSIONS
  This large cohort study found no evidence of an increased risk of fetal death associated with exposure to an adjuvanted pandemic A/H1N1 2009 influenza vaccine during pregnancy.
authors.affiliation: Department of Epidemiology Research, Statens Serum Institut, Artillerivej 5, 2300 Copenhagen, Denmark. bjp@ssi.dk
authors.forename: Björn
authors.initials: B
authors.lastname: Pasternak
authors.forename: Henrik
authors.initials: H
authors.lastname: Svanström
authors.forename: Ditte
authors.initials: D
authors.lastname: Mølgaard-Nielsen
authors.forename: Tyra G
authors.initials: TG
authors.lastname: Krause
authors.forename: Hanne-Dorthe
authors.initials: HD
authors.lastname: Emborg
authors.forename: Mads
authors.initials: M
authors.lastname: Melbye
authors.forename: Anders
authors.initials: A
authors.lastname: Hviid
mesh_terms: D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D005260:Female; D046689:Fetal Mortality; D006801:Humans; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000009:adverse effects*; D007251:Influenza, Human / Q000453:epidemiology / Q000517:prevention & control*; D053208:Kaplan-Meier Estimate; D058873:Pandemics / Q000517:prevention & control*; D011247:Pregnancy; D011248:Pregnancy Complications / Q000517:prevention & control
chemical_list: D007252:Influenza Vaccines; C556153:pandemrix