Pandemic influenza in pregnant women
Pandemic (H1N1) 2009 briefing note 5
31 July 2009 | GENEVA - Research conducted in the USA and published 29 July in The Lancet  has drawn attention to an increased risk of severe or fatal illness in pregnant women when infected with the H1N1 pandemic virus.
Several other countries experiencing widespread transmission of the pandemic virus have similarly reported an increased risk in pregnant women, particularly during the second and third trimesters of pregnancy. An increased risk of fetal death or spontaneous abortions in infected women has also been reported.
Increased risk for pregnant women
Evidence from previous pandemics further supports the conclusion that pregnant women are at heightened risk.
While pregnant women are also at increased risk during epidemics of seasonal influenza, the risk takes on added importance in the current pandemic, which continues to affect a younger age group than that seen during seasonal epidemics.
WHO strongly recommends that, in areas where infection with the H1N1 virus is widespread, pregnant women, and the clinicians treating them, be alert to symptoms of influenza-like illness.
WHO recommendations for treatment
Treatment with the antiviral drug oseltamivir should be administered as soon as possible after symptom onset. As the benefits of oseltamivir are greatest when administered within 48 hours after symptom onset, clinicians should initiate treatment immediately and not wait for the results of laboratory tests.
While treatment within 48 hours of symptom onset brings the greatest benefits, later initiation of treatment may also be beneficial. Clinical benefits associated with oseltamivir treatment include a reduced risk of pneumonia (one of the most frequently reported causes of death in infected people) and a reduced need for hospitalization.
WHO has further recommended that, when pandemic vaccines become available, health authorities should consider making pregnant women a priority group for immunization.
Danger signs in all patients
Worldwide, the majority of patients infected with the pandemic virus continue to experience mild symptoms and recover fully within a week, even in the absence of any medical treatment. Monitoring of viruses from multiple outbreaks has detected no evidence of change in the ability of the virus to spread or to cause severe illness.
In addition to the enhanced risk documented in pregnant women, groups at increased risk of severe or fatal illness include people with underlying medical conditions, most notably chronic lung disease (including asthma), cardiovascular disease, diabetes, and immunosuppression. Some preliminary studies suggest that obesity, and especially extreme obesity, may be a risk factor for more severe disease.
Within this largely reassuring picture, a small number of otherwise healthy people, usually under the age of 50 years, experience very rapid progression to severe and often fatal illness, characterized by severe pneumonia that destroys the lung tissue, and the failure of multiple organs. No factors that can predict this pattern of severe disease have yet been identified, though studies are under way.
Clinicians, patients, and those providing home-based care need to be alert to danger signs that can signal progression to more severe disease. As progression can be very rapid, medical attention should be sought when any of the following danger signs appear in a person with confirmed or suspected H1N1 infection:
- shortness of breath, either during physical activity or while resting
- difficulty in breathing
- turning blue
- bloody or coloured sputum
- chest pain
- altered mental status
- high fever that persists beyond 3 days
- low blood pressure.
In children, danger signs include fast or difficult breathing, lack of alertness, difficulty in waking up, and little or no desire to play.
 Jamieson DG et al. H1N1 2009 influenza virus infection during pregnancy in the USA. Lancet. 2009 Aug 8;374(9688):429-30; published online July 29, 2009