This literature review summarises many research articles on the subject. It reports that women who exercise during pregnancy reduce their risk of gestational diabetes by approximately 50% and the risk of pre-eclampsia by about 40%, compared to inactive women. The review also suggests that about 30 minutes per day of moderate-intensity physical activity during pregnancy may be sufficient to reduce the risk of gestational diabetes. There is also a strong link between regular exercise and improved emotional well-being and reduction in stress and anxiety. It is thought that the drop in pre-eclampsia risk is, at least in part, due to the psychological benefits of regular physical activity.
[J. Dempsey, C. Butler & A. Williams: No Need for a Pregnant Pause: Physical Activity May Reduce the Occurrence of Gestational Diabetes Mellitus and Preeclampsia in: Exercise and Sport Sciences Reviews (2005) vol. 33, no. 3, pp.141-149.]