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INTRODUCTION/BACKGROUND

KEY QUESTIONS

  • How does pregnancy affect maternal respiratory physiology?

  • What are the effects of pregnancy on asthma?

  • What are the risks associated with asthma in pregnancy, and how do you mitigate those risks?

  • What is the safety of pharmacologic agents used to maintain asthma control in pregnancy?

CASE 20-1

A 25-year-old nonsmoking pregnant female (gravida 1, para 0) at 12 weeks estimated gestation, with history of asthma since childhood, presents with several months of worsening symptoms of wheezing and dyspnea, which now occur daily, requiring daily use of her albuterol and awakening her from sleep one to two nights per week. Her husband had adopted a pet cat six months prior. Her symptoms are triggered when she performs household cleaning. Spirometry revealed forced expiratory volume in 1 second (FEV1) 76% of predicted value, which increased to 90% after administration of albuterol.

Asthma is a common chronic disorder of the airways characterized by variable and recurring symptoms and involving a complex interaction of airflow obstruction, bronchial hyperresponsiveness, and an underlying inflammation.1

EPIDEMIOLOGY

Asthma is reported to be one of the most common serious medical conditions to complicate pregnancy, and the prevalence of self-reported asthma in the United States is between 8.4% and 8.8%.2 In a prospective study of 366 pregnancies in 330 women with asthma, asthma worsened in 35% of the women, improved in 28%, and remained unchanged in 33%. Asthma was significantly less frequent and severe during the last 4 weeks of pregnancy than during any other gestational interval.

In women whose asthma improved during pregnancy, the improvement was gradual with progressive pregnancy, whereas in women whose asthma worsened during pregnancy, there was an increase in asthma symptoms at between 29 and 36 weeks gestation. Asthma symptoms were uncommon during labor and delivery (L&D), occurring in only 10% of women, with approximately equal proportions of these women receiving either no treatment or inhaled bronchodilators. Asthma reverted to its prepregnancy course at 3 months postpartum in 73% of women. In 34 subjects prospectively studied for two successive pregnancies, significant concordance between the asthma course during the first and second pregnancies was observed.3

PATHOPHYSIOLOGY

The dominant physiological event leading to clinical symptoms in asthma is airway narrowing, which subsequently interferes with airflow. Bronchial smooth muscle contraction (bronchoconstriction) occurs quickly during acute exacerbations of asthma, narrowing the airways, in response to exposure to a variety of stimuli, including allergens or irritants. Allergen-induced acute bronchoconstriction results from immunoglobulin E (IgE)–dependent release of mediators, which include histamine, tryptase, leukotrienes, and prostaglandins that directly contract airway smooth muscle, from mast cells.4 As the disease becomes more persistent and inflammation more progressive, further airflow limitation occurs due to factors such as edema, inflammation, mucus hypersecretion, and the formation of inspissated mucus plugs as well as structural changes, including hypertrophy and hyperplasia of ...

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