What instruction should a nurse give to a patient scheduled for amniocentesis at 18 weeks pregnant?

The correct instruction for a patient scheduled for amniocentesis at 18 weeks pregnant is to empty her bladder prior to the test. This recommendation is vital because having a full bladder provides better visualization of the uterus and positioning of the fetus during the procedure. A distended bladder pushes the uterus upward and helps to create a clearer pathway for the needle to access the amniotic sac safely. Additionally, it minimizes the risk of inadvertently puncturing the bladder during the procedure, which can lead to complications.

The other options may not be appropriate in this context. For instance, resting for at least 30 minutes after the test can be helpful for overall recovery, but it is not a necessary instructional priority prior to the amniocentesis itself. Drinking plenty of water before the test is not needed and could lead to discomfort if the bladder is overly full. Similarly, eating a light snack is typically not required for this specific procedure and does not directly contribute to its safety or efficacy. The primary concern is ensuring the bladder is emptied for optimal results during the amniocentesis.