Asthma is one of the most common medical complications of pregnancy. Asthma control is associated with improved perinatal outcomes. Peak flow measures have been recommended to determine the status of asthma, yet norms for peak flow values in women with asthma are missing from the literature. The purpose of this study was to determine average peak flow values in pregnant women with asthma. Forty-three women were recruited into the study prior to the 20th week of pregnancy. Demographic data, including age, ethnic background, and number of pregnancies, were collected. Type and severity of asthma, medications used for asthma, and past hospitalizations for asthma were recorded. Peak flow values increased across the three trimesters. Significant differences were found in peak flow values between the first and third trimesters (>.001) and the second and third trimesters (>.007). Findings from the present study contradict those of studies on pregnant women without asthma.