There is no uniform standard for the weight of pregnant women in their 6th month of pregnancy. Because the physical condition of each pregnant woman before pregnancy is different, the weight gain after pregnancy is generally judged by the body mass index before pregnancy, i.e. BMI = weight (kg) / height (m).2 The BMI values of adults are divided into underweight BMI <18.5, normal BMI = 18.5-23.9, and overweight BMI >24. If a pregnant woman is underweight before pregnancy, it is recommended that she gain 0.5kg per week from the middle to the end of pregnancy. If a pregnant woman is of normal weight before pregnancy, it is recommended that she gain 0.4kg per week in the middle and late stages of pregnancy, so that she gains about 4-5kg in the 6th month of pregnancy. During pregnancy, pregnant women should pay attention to monitor their weight, if the weight gain is rapid, they should control their diet reasonably and exercise moderately, so as to slow down the weight gain while ensuring the normal development of the fetus. If the weight gain is low and the fetus is growing slowly, attention should be paid to increasing nutrition and eating a diet rich in high quality protein and nutrients so as to promote healthy fetal growth and development.