Women with a normal prepregnancy body mass index (BMI) and those who meet the recommended weight gains are healthiest and have healthier children. Adequate gestational weight gain contributes to better perinatal short- and long-term health outcomes in both mothers and infants. However, many key aspects of the health of women of childbearing age have changed, including a high prepregnancy BMI and advanced age, along with a high proportion of women from diverse ethnicities. Overweight and obesity have become major problems in the world. High prepregnancy BMI, overweight and obesity, are risk factors for adverse pregnancy outcomes, such as gestational diabetes, preeclampsia, cesarean delivery, and having a macrosomic infant. On the other hand, underweight is associated with a higher incidence of miscarriage, and the delivery of small for gestational age (SGA) and low birth weight (LBW) infant. Prepregnancy BMI and gestational weight gain show strong association with pregnancy outcomes. Their combined effects on maternal and neonatal outcomes, including short- and long-term health risks, are strong. Therefore, it is important that health providers help women implement lifestyle changes to achieve normal BMI levels preconception, avoid excess weight gain during pregnancy and eliminate postpartum weight retention.