假如我们在生时长30磅，这30磅时这样分配的（应该是参考数据）：
7 1/2pounds is about how much the baby will weigh by the end of pregnancy
1 1/2pounds is how much the placenta weighs
4 pounds is attributed to increased fluid volume
2 pounds is the weight of the uterus
2 pounds is the weight of breast tissue
4 pounds is because of increased blood volume
7 pounds is attributed to maternal stores of nutrients and muscle development
2 pounds for the amniotic fluid
Total: 30 pounds
