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How does the uterus change in size and shape during pregnancy?

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Close-up of a home pregnancy test device showing a blue plus sign in the result window, indicating a positive result for pregnancy. — pregnancy Devices for individual use at home detect pregnancy by measuring levels of the hormone human chorionic gonadotropin (hCG) in urine.

During pregnancy, the uterus undergoes dramatic transformations to accommodate the developing fetus. In a nonpregnant state, the uterus is a thick-walled, pear-shaped organ measuring approximately 7 cm in length and weighing about 30 grams. By the end of pregnancy, it expands into a large, thin-walled, elastic, fluid-filled cylinder that measures about 30 cm in length and weighs approximately 1,200 grams, with a capacity of 4,000 to 5,000 ml.1

The change in size is driven by a marked increase in the number of muscle fibers, blood vessels, and lymphatic vessels, as well as a five- to tenfold increase in the size of individual muscle fibers. Regarding shape, the uterus remains largely unchanged during the first few weeks but gradually softens. By the 14th week, it forms a flattened or oblate spheroid. As the pregnancy progresses, the lower part of the corpus (the isthmus) stretches and unfolds to form the lower uterine segment. Eventually, the uterus rises out of the pelvis to fill the abdominal cavity, often rotating to the right due to the position of the bowel.1