Approximately 6 percent of pregnant women have asthma, making this one of the most common potentially serious medical complications of pregnancy. Some studies have reported a higher rate of preterm births to asthmatic mothers, but these results have not been consistent, and studies have not been stratified for the severity of asthma and other factors. Dombrowski and colleagues studied the relationship of different severities of maternal asthma to preterm delivery and other adverse perinatal outcomes.

This prospective, cohort study involved women at 16 university medical centers over a four-year period. The researchers enrolled 906 women with mild asthma, 906 with moderate to severe asthma, and 928 control patients. The groups were balanced at recruitment for smoking status and ethnicity. Exclusions from the study included multiple gestation, congenital abnormality in the fetus, other maternal pulmonary disease, and inability to accurately estimate gestation. Demographic and obstetric data were collected at enrollment, and spirometry was performed on participants with asthma. The mothers were followed every month until delivery. At each visit, forced expiratory volume in one second was obtained, and information was collected about symptoms and medication use.

Complete data were obtained on 866 mothers with moderate to severe asthma, 873 with mild asthma, and 881 control patients. The rates of asthma exacerbation during follow-up in mothers with mild, moderate, and severe asthma were 12.6, 25.7, and 51.9 percent, respectively. Overall, 23 percent of mothers reported a decrease in severity of asthma, while 30.3 percent reported an increase in symptom severity. No significant differences were apparent among the groups in any pregnancy outcomes except for wheezing during labor and neonatal sepsis.

When pregnancy outcomes in mothers with severe asthma were compared with those of control patients, a significantly increased risk of gestational diabetes and delivery before 37 weeks of gestation was found. The adjusted odds ratio (OR) for gestational diabetes was 3.0 and that for delivery before 37 weeks of gestation was 2.2. The rate of cesarean delivery was also increased (OR, 1.6).

The authors conclude that asthma is not associated with adverse pregnancy outcomes except for neonatal sepsis. Mothers with the most severe asthma appear to be at greatest risk of adverse outcomes, especially gestational diabetes, preterm delivery, and cesarean delivery.

editor’s note: The authors caution that the women studied were mainly inner-city residents and that the results may not be applicable to all women with asthma. In addition, they monitored only immediate pregnancy outcomes. The long-term effects of fetal hypoxia, anti-asthma medications, and other aspects of asthma on the infants are unknown. From a family medicine perspective, the facts that nearly 19 percent of the asthmatic mothers smoked, their average body mass index was nearly 28, and most did not present for obstetric care until 19 weeks of gestation also are of interest. More prospective care is needed to help women begin pregnancy in the healthiest condition possible.—a.d.w.