Maternal pregravid obesity is associated with adverse outcomes in pregnancy. There are many complications by maternal obesity during pregnancy, such as spontaneous abortion, congenital malformations, gestational hypertention, preeclampsia, gestational diabetes mellitus, fetal macrosomia, and so on. Also, at parturition, the prevalence of cesarean section and associated complications such as deep vein thrombosis, wound disruption, and infection increase. Furthermore, offspring of obese women increases the risk of adolescent components of the metabolic syndrome. To improve short- and long-term adverse outcome associated with obese pregnant women, we need to encourage obese women to lose body weight before pregnancy. During pregnancy, weight gain should be limited to Institute of Medicine guidelines.