The exact reason for this is unknown, but the increase in the body's cortizone level during pregnancy may be an important cause of the improvement which can occur. Then again, asthma symptoms may be worse during pregnancy. Some women experience gastroesophageal reflux causing belching and heartburn. This reflux, as well as sinus infections and increased stress, may aggravate asthma. Asthma has a tendancy to worsen during pregnancy in the late second and early third trimester.
Many women experience less asthma during the last four weeks of pregnancy.
Troublesome asthma during labor and delivery is extremely rare in women whose asthma has been adequately controlled during pregnancy. Most asthmatic women are even able to perform the Lamaze breathing techniques during delivery without difficulty. The increase in plasma epinephrine that occurs during labor and delivery may contribute to the absence of asthma symptoms during this critical time period. Some studies suggest that the pattern that asthma symptoms follow initially may be reported in subsequent pregnancies. When problems do occur, we counter them by an appropriate change in the management program.