Obesity during pregnancy is not without consequences, and obesity-related complications are an important burden for obstetrical care providers. Obesity is associated with several reproductive disturbances. Body weight influences the timing of menarche and the capacity to achieve pregnancy. Early reproductive dysfunction among obese women includes precocious menarche, irregular menstrual cycles, oligomenorrhea and amenorrhea, and chronic anovulation. This chapter covers the antepartum complications, effects of obesity on fertility and early pregnancy, intrapartum complications, fetal complications, and postpartum complications. Obesity causes significant complications during pregnancy for the mother and fetus. Interventions promoting prepregnancy weight loss and the prevention of excessive weight gain during pregnancy must begin in the preconception period.