title: Incidence and risk factors for exacerbations of asthma during pregnancy.
abstract: BACKGROUND
  Asthma is one of the most common chronic diseases among pregnant women. Acute exacerbations of asthma during pregnancy have an unfavorable impact on pregnancy outcome. This review provides an overview of current knowledge of incidence, mechanisms, and risk factors for acute exacerbations of asthma during pregnancy.
  
  
  METHODS
  A narrative literature review was carried out using the PubMed database.
  
  
  RESULTS
  During pregnancy, up to 6% of women with asthma are hospitalized for an acute exacerbation. The maternal immune system is characterized by a very high T-helper-2:T-helper-1 cytokine ratio during pregnancy and thereby provides an environment essential for fetal survival but one that may aggravate asthma. Cells of the innate immune system such as monocytes and neutrophils are also increased during pregnancy, and this too can exacerbate maternal asthma. Severe or difficult-to-control asthma appears to be the major risk factor for exacerbations during pregnancy, but studies also suggest that nonadherence with controller medication and viral infections are important triggers of exacerbations during pregnancy. So far, inconsistent findings have been reported regarding the effect of fetal sex on exacerbations during pregnancy. Other risk factors for exacerbation during pregnancy include obesity, ethnicity, and reflux, whereas atopy does not appear to be a risk factor.
  
  
  CONCLUSIONS
  The incidence of asthma exacerbations during pregnancy is disturbingly high. Severe asthma - better described as difficult-to-control asthma - nonadherence with controller therapy, viral infections, obesity, and ethnicity are likely to be important risk factors for exacerbations of asthma during pregnancy, whereas inconsistent findings have been reported with regard to the importance of sex of the fetus.
authors.affiliation: Department of Pulmonary Medicine, Hvidovre Hospital and University of Copenhagen, Copenhagen, Denmark.
authors.forename: Zarqa
authors.initials: Z
authors.lastname: Ali
authors.forename: Charlotte Suppli
authors.initials: CS
authors.lastname: Ulrik
keywords: acute exacerbations; asthma severity; incidence; pregnancy; risk factors