The organ that changes the most during pregnancy is the uterus, as follows: 1. weight, the uterus weighs 50g when non-pregnant, up to 1100g at full term; 2. volume, the volume of the uterus is 15mL when non-pregnant, up to 20mL or greater at full term, 500-1000 times that of non-pregnancy; 3. volume, the size of the uterus is 8×5×3cm when non-pregnant, the volume of the uterus is 35×25×22cm at full term. The uterus increases uniformly in early pregnancy, and the uterine base increases fastest in late pregnancy, the increase of the uterus is mainly due to the increase and lengthening of the myocytes, which are 20nm long and 2nm wide when non-pregnant, 500nm long and 10nm wide at full term, the thickness of the uterine muscle wall is about 1cm when non-pregnant, 2-2.5cm thick in mid-pregnancy, and thinner at full term, 1.0-1.5cm; 4. The uterine isthmus is 1cm long in non-pregnancy and stretches to 7-10cm after term; 5. The endometrium is called meconium after pregnancy.