Pregnant mothers do not grow in weight but the fetus has been large according to the reasons for analysis, pregnant women did not grow in weight but the fetus is large most of the placenta may be good function or due to pregnant women have gestational diabetes. 1. good placental function: when a pregnant woman placenta function is good, this time the placenta blood supply, oxygen supply is better, the fetus can absorb rich oxygen and nutrition, resulting in fast growth, easy to big. 2. Gestational diabetes: when pregnant women with gestational diabetes, because of their own high blood sugar, the fetus is easy to absorb too much sugar, resulting in rapid growth of the fetus, and even the development of a huge child may be. In addition, if the parents are tall, the fetus is large genetic factors, is normal, pregnancy attention should be timely observation of fetal growth changes, if it has been large to be combined with the cause to take the right measures to treat.