Final answer:
At 20 weeks of gestation, the top of the uterus, or fundus, is usually at the same level as the mother's belly button. This expansion of the uterus accommodates the growing fetus, which at this stage is about 30 cm (12 inches) long.
Step-by-step explanation:
The uterus, or womb, is a vital reproductive organ that undergoes significant changes during pregnancy to support the development of the fetus. At 20 weeks of gestation, the uterus expands to accommodate the growing fetus. This expansion is both upward and outward from its original position.
Normally, around the 20-week mark, the top of the uterus (called the fundus) can be found at about the level of the mother's belly button (umbilicus). This is a general guideline, as the position can be influenced by a variety of factors including maternal body type, number of pregnancies, and the presence of fibroids or other conditions.
During pregnancy, the uterus grows from the size of a woman's fist to become large enough to hold a developing baby. By 20 weeks, the fetus itself is about 30 cm (12 inches) long, and the mother often feels its first movements. The uterus's increased size at this point in pregnancy is due to the growth of the fetus and the expansion of the uterine walls to provide space and nutrients for the baby.