The normal non-pregnant uterus is only 6 to 8 centimeters long, weighs only more than 50 grams, and the capacity of the uterine cavity is only 5 milliliters. How can such a small uterus be enlarged to accommodate a fetus weighing 3 to 4 kilograms?
This is mainly because after pregnancy, the placenta gradually forms and secretes hormones, such as protein hormones and steroid hormones, including human chorionic gonadotropin, placental prolactin, chorionic thyroid-stimulating hormone, and estrogen. and progesterone, etc. Under the influence of these hormones, a series of changes occur in various systems throughout the body. The reproductive system changes greatly, and the growth of the uterus in terms of weight, capacity, and volume is amazing. The capacity of the uterine cavity can reach about 5,000 ml during full-term pregnancy, which is 1,000 times that during non-pregnancy. In patients with polyhydramnios, it can reach 10,000 ml. The weight of the uterus can increase to 1,000 grams during full-term pregnancy, which is 20 times the original weight. Uterine enlargement is mainly caused by the hypertrophy and proliferation of uterine muscle cells (which can increase by more than 20 times), the dark growth of connective tissue, the increase and thickening of blood vessels, etc. The enlargement of the uterus is initially caused by the stimulation of endocrine hormones; and after 3 months, it is mainly caused by the increase in intrauterine pressure. In addition to the increase in size of the uterus, the shape of the uterus also changes with the increase of pregnancy months, from the original pear shape to a spherical or straight oval shape. The uterine muscle wall is about 1 cm thick when not pregnant; it gradually thickens to 2 to 2.5 cm in the second trimester; and gradually thins to 0.5 to 1 cm in the third trimester due to the further increase in uterine capacity.
The above are the changes in the uterus throughout pregnancy. Knowing these changes, it is not surprising that a small uterus can accommodate a full-term fetus.
This article is provided by Baidu Reading and is excerpted from \”The Clear \”Conception\” Plan\” Author: Sun Jianqiu and Xie Yingbiao