pcb Cantu 2013.

Methods	Retrospective cohort study. Pregnancy‐related outcomes were observed retrospectively among vaccinated and non‐vaccinated women who received prenatal care and delivered within Birmingham healthcare system in order to establish if vaccination could represent a risk factor.
Participants	Women with singleton pregnancy during 2009‐10 pandemic and 2010‐11 season who had prenatal visit between October and end of December of each season at 1 of the 6 prenatal clinics in Birmingham, Alabama (USA) without suspected foetal abnormality. Altogether, 1094 vaccinated and 2010 non‐vaccinated pregnant women were included.
Interventions	Vaccination with a pH1N1 virus containing vaccine (not further specified) at any time during pregnancy in pandemic season 2009/10 and in 2010 to 2011 epidemic. Participants immunised exclusively with TIV in 2009/10 season were excluded from the primary analysis. Vaccination status was ascertained through perinatal record system and vaccination logs. Women who were immunised outside of healthcare system were included if they were able to provide their vaccination date.
Outcomes	The following outcomes were collected and recorded at the time of care at the centres. Primary composite outcome: includes miscarriage, stillbirth, preterm birth < 37 weeks, and neonatal demise Miscarriage: defined as delivery prior to 20 weeks Preterm birth (< 37 weeks) Birth weight < 2500 g Neonatal demise (20 weeks) Stillbirth: defined as delivery of a non‐viable foetus at or after 20 weeks Pre‐eclampsia Small for gestational age: foetal growth less than the 10th percentile Neonatal intensive care unit admission Length of maternal stay Antiviral (oseltamivir) therapy
Notes	Funding source ‐ government Results and effect estimates are provided for both seasons pooled. Study population was limited to women with prenatal visit in the early flu season between 1 October and 31 December each year, when the vast majority of vaccines were given in order to assure that vaccinated and unvaccinated groups had similar exposure periods and avoid potential bias.
Risk of bias
Bias	Authors' judgement	Support for judgement
PCS/RCS ‐ selection exposed cohort All outcomes	Low risk	Representative of a pregnant women population belonging to the Birmingham healthcare system
PCS/RCS ‐ selection non‐exposed cohort All outcomes	Low risk	Drawn from the same population as the exposed cohort
PCS/RCS ‐ comparability All outcomes	Low risk	Possible confounders have been taken into account.
PCS/RCS ‐ assessment of outcome All outcomes	Low risk	Secure record
Summary assessment	Low risk	Low risk of bias