Substantial proportion of women stop exercising after they discover they are pregnant, and only few begin participating in exercise activities during pregnancy. The adoption or continuation of a sedentary lifestyle during pregnancy may contribute to the development of certain disorders. In view of the global epidemic of sedentary behaviour and obesity-related pathology, prenatal physical activity was shown to be useful for the prevention and treatment of these conditions. The aim of this study was to investigate the changes in the cardiorespiratory fitness of exercising pregnant women in Rivers State University Teaching Hospital. This original research article is designed using randomized pre test-post test control group. The differences in the pre-test and post-test values represented the impact of the ten (10) weeks aerobics training on the experimental group. Sixty-four pregnant women who completed the study were simply randomized into experimental (n=38) and control (n=26) groups and their pre-intervention values of systolic blood pressure, diastolic blood pressure, peak expiratory flow rate and resting heart rate were taken and recorded. A ten week, three times weekly aerobic exercise (40 – 45 minutes) training was administered on the experimental group. A post-intervention score was also taken from all participants and the data analyzed using mean and standard deviations. Analysis of covariance was used to determine the changes at 0.05 alpha level. Results showed the Aerobic Exercise Training impacted – Systolic Blood Pressure of pregnant women (experimental 125.47+78.05 and control 130.23+8.92). The Diastolic Blood Pressure of the pregnant women (post intervention experimental score 65.47+5.0 and control 78.19+10.72. Heart rate of the pregnant women decreased in the experimental group though insignificantly (experimental 89.87+6.51 and control 91.46+6.56). The expiratory peak flow rate increased from 261.58+80.39 to 329.74+66.07 and in the control group 203.85+66.07 to 204.62+22.84. From the foregoing, it was concluded that there were positive changes in the cardiorespiratory fitness of exercising pregnant women leading to delivery.