Final answer:
The position when the surgeon chooses an open approach for emergent surgery for ectopic pregnancy in a pregnant woman is the Supine position.
Step-by-step explanation:
The position when the surgeon chooses an open approach for emergent surgery for ectopic pregnancy in a 29-year old pregnant woman with severe lower abdominal pain and slight vaginal bleeding is the Supine position. In the supine position, the patient lies flat on their back, with the legs extended and arms to the side. This position allows for better access to the abdomen during surgery.