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Asthma during pregnancy can be life-threatening. So counsel patients not to stop taking asthma drugs; most are not harmful to a fetus.
Although fewer women are dying from asthma, both the disease and its complications during pregnancy are increasing, according to the American College of Obstetricians and Gynecologists, which earlier this year released new evidence-based recommendations on managing asthma in pregnancy.1 Based on an assessment of existing studies on asthma and pregnancy, the new guidelines support the findings of the National Asthma Education Prevention Program.
We sometimes forget that we graduated from medical school before we became specialists. It's important not only that we maintain our basic knowledge of diseases such as asthma and their pathophysiology, but also keep up with new recommendations. How often does a frustrated patient tell us her primary-care physician is refusing to prescribe a medication or treat a common problem because she is pregnant? As physicians for women's health, we need not be experts in the field of asthma, but we must be familiar enough with this and other diseases that can coexist with pregnancy to guide and encourage primary-care physicians to work with us in caring for our pregnant patients.
Asthma is one of the most common potentially serious conditions that can complicate pregnancy. Its estimated prevalence among pregnant women 18- to 44-years old is up to 9%.1,2 But it's up to 12% in younger pregnant women aged 18 to 24.2 The chances of ever receiving a diagnosis of asthma doubled between 1998 and 2002. According to the National Health Interview Survey conducted from 1997 to 2003, 38.5% of pregnant women who carry an asthma diagnosis reported at least one asthma attack in the previous year,2 which suggests that many patients are not being adequately managed. These data, however, were based on self-reporting and were not corroborated by a physician.
Recently, however, the Maternal Fetal Medicine Unit (MFMU) published a prospective observational study that identified few significant differences between women with and without asthma. This study evaluated preterm delivery, gestational diabetes, preeclampsia, preterm labor, chorioamnionitis, oligohydramnios, cesarean delivery, low birthweight, small-for-gestational-age, and congenital malformations in women with and without asthma. Among 2,620 women, however, the only statistically significant difference in outcome was an increased cesarean delivery rate in women with moderate-to-severe asthma.4 Although the MFMU states there are no real issues, other studies have reported pregnancy complications.5-7
When interpreting the study results of asthma in pregnancy, one must be aware of many considerations: although the results of these prospective studies are reassuring in their consensus of good pregnancy outcomes, they don't mean that asthma should be considered benign because active asthma management was a part of these studies and may have had a positive impact on the outcomes. Similarly, women who enroll in research studies tend to be more vigilant regarding their health care and more adherent to therapy. The lack of adverse outcomes associated with severe asthma is potentially due to the small numbers of women in that category, and therefore there was likely insufficient power to detect significant results.1
Generally throughout pregnancy, asthma severity stays the same in one third of patients, improves in one third of patients, and worsens in one third.8-11 It should come as no surprise that those with severe disease before becoming pregnant are more likely to deteriorate,11 but even mild disease can cause complications. (For example, one group of researchers reported a 12.6% exacerbation rate and a 2.3% hospitalization rate with mild asthma).12,13
Often, the course of disease will be similar from one pregnancy to the next. Proper medical control should allow a woman with asthma to maintain a pregnancy with little or no increased risk to herself or her fetus.14 In fact, as ACOG and others point out, it is probably safer for a pregnant woman to be treated with asthma medications than for her pregnancy to be riddled with asthma exacerbations.