The course of asthma is changed by pregnancy in variable ways for unknown reasons. Although the prospective studies used different criteria to stratify the severity of the patients' asthma, their conclusions were remarkably similar. Over-all, an equal number of women have asthma symptoms that improve, worsen, or are unchanged through pregnancy. Asthma symptoms can worsen during pregnancy because of identifiable factors, such as infection, gastroesophageal re-flux disease, reduction of appropriate medications by physician or patient, and smoking. Undertreatment, which remains a problem during pregnancy, can lead to continued difficulty with asthma. Severe asthmatics tend to have increased symptoms compared with mild asthmatics. If symptoms worsen, it usually occurs in the second and third trimesters, with the peak in the sixth month. Generally, there is improvement in asthma in the last 4 weeks of pregnancy. During labor and delivery, only 10% to 20% of asthmatics have symptoms;severe asthmatics are more likely to have exacerbations. Asthma tends to return to the prepregnancy state within 3 months post partum. Successive pregnancies tend to have a similar course in each individual. Every asthmatic woman should be maintained on appropriate medications and followed carefully throughout pregnancy, especially in the second and third trimesters. Asthma specialists should be available for collaborative care when asthma is uncontrolled, or if there is an exacerbation. A timely adjustment in treatment for any changes in asthma course that might occur ensures the best control of the disease in the face of complex multiple influences.