Asthma is the most common chronic condition associated with complications during pregnancy and carries an increased risk of poor outcomes for the fetus. Studies have indicated that at least one in five women with asthma experience a severe exacerbation during pregnancy, rising to more than one half in women with severe asthma. The relationship between severity of asthma during pregnancy and perinatal outcomes is unclear. Some studies have shown an association between hospitalization for asthma during pregnancy and low birth weight of the neonate, whereas in others there was no correlation between birth weight and acute asthmatic attacks during pregnancy. Murphy and colleagues evaluated asthma exacerbations in 146 Australian women enrolled in a prospective cohort study of asthma to establish the rate of severe exacerbations during pregnancy and investigate the relationship between exacerbation rate and perinatal fetal outcomes.

The participants included all consenting women who were pregnant and had asthma and who made two or more antenatal visits to a university clinic. An intake assessment was performed, with a detailed history, pulmonary function testing, physical examination, and laboratory investigations. Prepregnancy asthma was classified as mild, moderate, or severe using national guidelines based on history, symptom severity and frequency, medication use, and pulmonary testing (e.g., forced expiratory volume and peak expiratory flow). The asthma history was repeated at each clinic visit, and the participants were monitored for exacerbations. A mild exacerbation, or loss of control, was defined as an episode managed by the patient and characterized by an increase in symptoms or medication use, or a period of decreased peak flow on home monitoring. An exacerbation was defined as severe if it required hospital admission, emergency department treatment, an unscheduled physician appointment, or a course of oral steroid therapy. The main outcome measured was the frequency and severity of exacerbations during pregnancy; fetal outcomes, principally birth weight, also were examined.

Overall, 55 percent of participants had an exacerbation of asthma during pregnancy. Severe exacerbations occurred in 53 women (36 percent) at a mean gestation of 25 weeks. Mild exacerbations were documented in 34 women (23 percent) at a median gestation of 28.5 weeks. Seven women reported mild and severe exacerbations. Eight percent of women with mild asthma before pregnancy experienced severe exacerbations during pregnancy compared with 47 percent of those with moderate background asthma and 65 percent of those with severe background asthma. Nineteen of 49 women (39 percent) who had severe asthma before pregnancy required oral steroids during pregnancy, and nine women (18 percent) required hospital admission. The differences between the severe and mild groups were statistically significant.

No statistically significant differences were found in overall pregnancy outcomes between women who experienced a severe exacerbation of asthma during pregnancy and those who did not, although there was a trend toward lower neonate birth weight in women who had a severe exacerbation. Subgroup analysis showed a significantly decreased birth weight in male neonates whose mothers had a severe exacerbation. Women who had a severe exacerbation gained less weight but did not differ from other participants in any other significant variable. Factors associated with exacerbations included the winter season (43 percent of exacerbations), possible viral infection (34 percent), smoking (28 percent), and nonadherence to inhaled corticosteroid medication (29 percent).

The authors conclude that women with asthma experience an increased rate of exacerbations during pregnancy and require substantial medical interventions. The rate of severe exacerbations is highest in mothers with the most severe prepregnancy asthma. Viral infections and nonadherence to medications appear to be common causes. The study was too small to establish significant relationships between exacerbations of asthma and poor pregnancy outcomes, but it showed significantly reduced birth weight in male infants.