The obesity epidemic affects all, including women of reproductive age. One in five women attending prenatal care in the UK is obese. Prepregnancy obesity is associated with serious short- and long-term complications for mother and child. Furthermore, gestational weight gain (GWG) of obese pregnant women generally exceeds the Institute of Medicine recommended ranges. This observation can partially be explained by an unbalanced diet and lack of daily physical activity. Despite this, few lifestyle intervention trials in obese pregnant women are available. Two out of seven intervention trials focusing on GWG, nutrition and physical activity, reached a significant decrease in GWG. Developing guidelines to promote appropriated weight gain and healthy lifestyle in overweight and obese pregnant women remains a challenge. This review aims to summarize the complications associated with maternal prepregnancy overweight and obesity and to discuss possible strategies to improve the lifestyle habits of pregnant women.