How can a nurse assist during an amniocentesis procedure?

When assisting during an amniocentesis procedure, it's crucial to ensure that the patient is positioned correctly for optimal access and comfort. Placing a drape that exposes only the abdomen is appropriate as it maintains the patient's modesty and focuses the medical team's attention on the area of the procedure. This also helps in preventing contamination and provides a clear view for the healthcare provider performing the amniocentesis.

The other options suggest actions that would either compromise the patient's comfort and safety or hinder the procedure. For instance, positioning the patient flat on their back without support could lead to discomfort and inadequate access for the procedure. Encouraging the patient to stand would be impractical, as it would not allow proper access to the abdomen and increases the risk of complications. Lastly, elevating both legs is unnecessary in this context, as it does not contribute to the successful outcome of an amniocentesis and could actually complicate positioning.