Final answer:
The nursing action to perform when assessing uterine position is to place a hand at the base of the uterus to prevent uterine descent.
Step-by-step explanation:
When preparing to palpate Rebecca's abdomen for uterine position, a nursing action to perform is to place a hand at the base of the uterus to prevent uterine descent. This helps in determining its position, size, and shape. By palpating the uterus, the nurse can assess for abnormalities such as fibroids, tumors, or an enlarged uterus.