pbb Irving 2013.

Methods	Case‐control study investigating the association between influenza immunisation during pregnancy and spontaneous abortion
Participants	Cases (n = 243) were identified from among the members of 6 Vaccine Safety Datalink organisations. Diagnoses of spontaneous abortion (ICD‐9 code 634) and unspecified abortion (ICD‐9 codes 637) assigned during the 2005 to 2006 and 2006 to 2007 seasons were reviewed and different diagnoses excluded. Controls (n = 243) were selected from among women who had confirmed intrauterine pregnancy and delivery after the 20th gestational week by frequency‐matching of last menstrual period (within 2 weeks) and healthcare organisation.
Interventions	Immunisation with influenza vaccine. Participants were considered exposed if they were immunised within 28 days before index date. Analysis considering whether vaccine exposure occurred during or before pregnancy was also performed.
Outcomes	Spontaneous abortion cases
Notes	Government funded
Risk of bias
Bias	Authors' judgement	Support for judgement
CC ‐ case selection All outcomes	Low risk	Consecutive series of cases from electronic databases
CC ‐ control selection All outcomes	Low risk	From the same population
CC ‐ comparability All outcomes	Unclear risk	Matched by LMP ‐ confounders
CC ‐ exposure All outcomes	Unclear risk	Medical record
Summary assessment	Unclear risk	Unclear