Although the 2009 H1N1 pandemic proved to be more benign than anticipated, it had a substantial effect on pregnant women. In the linked cohort study (doi:10.1136/bmj.d3214), Pierce and colleagues report the perinatal outcomes of 256 pregnant women admitted to hospital with H1N1 influenza in the United Kingdom.1

The study found that pregnant women admitted to hospital with H1N1 influenza had significantly higher rates of adverse pregnancy outcomes than uninfected pregnant women. These included three to four times higher rates of preterm birth, four to five times higher rates of stillbirth, and four to six times higher rates of neonatal death.1 These high rates of adverse perinatal outcomes were consistent with those reported in a population based study from the United States,2 which also found a high maternal death rate (five deaths in 489 pregnant women admitted to hospital). Presumably, details of specific maternal complications and causes of death will be forthcoming …