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How does the uterus change in size during pregnancy?

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human fetus; prenatal development — prenatal development An ultrasound image of a human fetus.

During pregnancy, the uterus undergoes significant physiological changes to accommodate the developing fetus. In a nonpregnant state, the uterus is a thick-walled, pear-shaped organ measuring approximately 7 cm (2.75 inches) in length and weighing about 30 grams (1 ounce). By the end of pregnancy, it transforms into a large, thin-walled, elastic, fluid-filled cylinder that can reach 30 cm (12 inches) in length, weigh approximately 1,200 grams (2.6 pounds), and hold a capacity of 4,000 to 5,000 ml.1

This dramatic enlargement is driven by several factors:
* Cellular growth: There is a marked increase in the number of muscle fibers, as well as a five- to tenfold increase in the size of individual muscle fibers.1
* Vascular and lymphatic expansion: The diameters of blood vessels, nerves, and lymphatic vessels within the uterine wall increase significantly to support the growing fetus.1
* Structural remodeling: The uterus rises out of the pelvis to fill the abdominal cavity. The lower portion of the corpus, known as the isthmus, stretches and unfolds to form the lower uterine segment, while the uterine wall thins as it stretches to contain the conceptus and amniotic fluid.1