Final answer:
The nurse is most concerned if a client plans to go on a strict diet to avoid gaining too much weight during pregnancy.
Step-by-step explanation:
The nurse is most concerned if a client makes the statement: 'I plan to go on a strict diet to avoid gaining too much weight.' During pregnancy, it is important for the mother to gain weight within a healthy range to ensure proper fetal growth and development. Restricting calories and going on a strict diet can deprive the fetus of essential nutrients and increase the risk of complications.