Final answer:
The best nursing action is to move a laboring woman from the supine position to a lateral position to optimize blood flow and fetal oxygenation.
Step-by-step explanation:
A laboring woman lying in the supine position may experience decreased blood flow to the uterus and placenta, a condition known as supine hypotensive syndrome, which can compromise fetal oxygen supply. The most appropriate nursing action is to assist the laboring woman into a lateral position, also known as the left-lateral or side-lying position. This position helps to alleviate pressure on the inferior vena cava and improve blood flow, thereby optimizing oxygen delivery to the fetus.