The uterus undergoes dramatic changes throughout a woman’s life, varying greatly with age. In infancy, it measures only 2–3 cm long. As a woman matures, its size and weight increase significantly: the nulliparous uterus is about 6–8 cm long and weighs 50–70 grams, while the parous uterus may reach 9–10 cm and weigh over 80 grams.
After puberty, the endometrium sheds cyclically, resulting in menstruation. During sexual intercourse, sperm travel through the uterine cavity to the fallopian tubes to fertilize an egg. Once conception occurs, the fertilized egg implants, grows, and develops within the uterine cavity. During childbirth, the uterus contracts to expel the fetus.
Why is the uterus capable of such functions?
The uterus is a hollow muscular organ. Its endometrium is a mucous membrane regulated by ovarian estrogen and progesterone, undergoing cyclic changes including proliferation, secretion, and shedding in response to hormonal fluctuations.
The uterine wall consists of highly developed smooth muscle rich in elastic fibers, giving it exceptional distensibility. Before pregnancy, the uterine capacity is merely 4–7 mL. By full-term pregnancy, the cavity holds the fetus, amniotic fluid, placenta, and other contents weighing more than 5000 grams — expanding its volume nearly 6000 times.
Uterine muscle also has powerful contractile ability. During labor, strong contractions thin and stretch the lower uterine segment, dilate the cervix, and push the fetus out. After delivery, sustained uterine contraction gradually returns the organ to its pre-pregnancy size.