The health benefits of physical exercise in the non-pregnant population are generally appreciated but its influence during pregnancy has not been clearly demonstrated. The focus of this proposal is to obtain for the first time a comprehensive understanding of the influence of regular physical exercise during pregnancy on cardiovascular, haemodynamic and autonomic nervous system (CHANS) parameters during pregnancy and following childbirth. This will involve assessing heart rate variability and cardiac stroke volume. This study will allow the investigators to compare CHANS parameters in pregnant women who are randomly assigned into three groups: a 'standard care' group and two groups who engage in a supervised programme of physical exercise (either land-based or water-based). The investigators will assess CHANS parameters at three stages during pregnancy and on one occasion following childbirth. This will allow the influence of regular (weekly) physical exercise on CHANS physiology to be assessed during advancing gestation. The investigators will thus use this study to provide initial evidence of the health benefits of regular and specific forms of antenatal physical exercise.