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Tuesday, April 3, 2007

Review: Asthma in pregnancy

Review: Asthma in pregnancy

This is the first in a series of occasional articles in the BMJ about how to manage a pre-existing medical condition during pregnancy. The article begins with a case scenario and addresses the following topics:

  • How common is asthma in pregnancy?
  • Does pregnancy affect asthma?
  • Does asthma affect pregnancy?
  • Management of asthma in pregnancy
  • Does asthma affect labour and delivery?
  • Does asthma affect postpartum period and breast feeding?
In terms of treatment, the article notes that it is safer to use asthma drugs in pregnancy than to leave asthma uncontrolled, as adverse perinatal outcomes are associated with uncontrolled asthma and reduced expiratory flow. Inhaled corticosteroids, theophylline, and short acting beta 2 agonists do not increase the risk of foetal congenital malformations, pre-eclampsia, preterm delivery, or low birth weight. The dose or regimen of asthma medications do not usually need to be changed in pregnancy.

Oral corticosteroids in the first trimester are associated with an increased risk of foetal cleft lip or palate. However, the increased incidence is small compared with the benefits of using such treatment and they should continue to be used in severe asthma and life threatening situations. Oral corticosteroids are also associated with preterm delivery and pre-eclampsia. Of note, 90% of prednisone is inactivated by the placenta, which limits foetal exposure and the risk of foetal withdrawal. Inhaled corticosteroids are safe in pregnancy, and they are not associated with foetal malformations or perinatal morbidity. Most studies in pregnancy have used budesonide, but the corticosteroid that was used successfully before pregnancy should be continued into childbirth.

Cromolyn sodium and short acting beta 2 agonists are safe to use during pregnancy. There are few data on long acting beta 2 agonists; salmeterol and formoterol have not been found to cause malformations, preterm delivery, or low birth weight in the limited number of women using them in prospective studies. Data on the safety of leukotriene modifiers in pregnancy are scarce therefore it seems reasonable to replace them with an inhaled corticosteroid at the start of pregnancy or with a long acting beta 2 agonist (if this is used as an "add on" therapy). Theophylline has been reported to be safe in human pregnancy at recommended doses; levels should be monitored because drug metabolism changes in pregnancy.

BMJ 2007; 334: 582-5 (link to extract)

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