Weight gain during pregnancy: A narrative review on the recent evidences.

Gestational weight gain is necessary for the normal fetus development, in fact a series of studies have evidenced that both low and excessive gestational weight gain is associated with negative fetal-neonatal outcomes. So, evidences on the optimal gestational weight gain across the ranges of the pre-pregnancy maternal body mass index are necessary. In this context, while for normal weight and underweight the recommendations of IOM are clearly stated and supported by well designed and conducted clinical studies, those for the obese pregnant women are even today debated. Pre-pregnancy obesity is associated with high risk to develop hypertension, gestational diabetes, cesarean section and high birth weight. The Institute of Medicine guidelines, in 2009, recommended that women with obesity gain 11-20 lb at a rate of 0.5 lb/week during the second and third trimesters of pregnancy. Successively, taking into account a series of meta-analysis, the American College of Obstetricians and Gynecologists emphasized that the IOM weight gain targets for obese pregnant women are too high. However the high risk to have babies small for gestational age, related to a low weight gain or a losing of weight during pregnancy, has also been demonstrated. More recent studies have taken into consideration the maternal and fetal outcomes of obese pregnant women with different obesity class (I,II,III) and different weight gain during pregnancy. The analysis of these studies, discussed in this narrative review, show that the appropriate gestational weight gain should be personalized considering the three obesity class; furthermore both an upper and lower limit of gestational weight gain should be reconsidered in order to prevent the negative maternal and fetal outcomes in these women.