Abstract: OBJECTIVE: No studies to date have examined the effect on Blood pressure (BP) when pregnant women participate in aquatic physiotherapy (AP) classes; although, previous studies have indicated that there may be a detrimental outcome to the pregnant mother and fetus when there is a significant rise in the maternal BP. At least three components may contribute to BP changes: temperature, exercise, and immersion. This study examines BP changes in pregnant women attending AP classes. METHOD: An experimental same-subject, repeated measures design was employed. Forty-five sets of data were collected from pregnant women attending routine, existing, nonaerobic AP classes. Blood pressure measurements were taken preimmersion, 2-5 minutes after entering the pool, immediately following the 50 minute AP class (while immersed), and 8-12 minutes after exiting the water. RESULTS: Systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP) data were analyzed using a repeated measures analysis of variance (ANOVA). For all sets of data a highly significant difference was observed (p = 0.0000). Post-hoc Tukey test results showed BP to decrease significantly on entering the water (MAP mean difference of 10.52 mm Hg, 95% CI 8.75 to 12.29), to remain at this low level postexercise while still immersed, and then return to preimmersion values 8-12 minutes after exiting the water. CONCLUSION: These results indicate that AP classes are safe for nonhypertensive pregnant women in their third trimester. The use of AP in the antenatal care of women with unstable BP or who are hypertensive needs further research.