Classic teaching is the rule of thirds in female asthmatics during pregnancy: 1/3 get better, 1/3 get worse and 1/3 stay the same. In general though, prior asthma severity predicts how bad asthma will be during pregnancy—if asthma was severe before pregnancy, it is often the same or worse during pregnancy.
Why do hormones affect allergy and asthma anyway? Why is the effect variable? It’s not an “allergy” to the hormone but it seems that estrogen and progesterone levels matter. Progesterone, the hormone of pregnancy, may:
- help asthma by promoting anti-inflammatory effects by the increase in serum free cortisol.
- help asthma by increasing breaths per minute and relaxing the muscles of the small airways which tighten in asthma
- or contribute to worsening asthma via changes in airway inflammation
The good news is that asthma exacerbations do not usually occur during labor and delivery. Most asthma flares seem to occur during the second trimester. The most important factor in avoiding asthma exacerbations, not surprisingly, is staying on your medications, especially inhaled steroids. Inhaled steroids and even oral or injected anti-inflammatory steroids are generally considered safe at every stage of pregnancy. In asthma, what’s good for the mother is good for the baby!
All asthma therapies are considered safe in pregnancy. Some medications (such as Pulmicort) are classified as pregnancy category B (studied in humans and considered safe). Most drugs, however, have a pregnancy category C designation which is stiil though of as safe but not as well studied.