Final answer:
Assess the client's dietary habits and nutritional intake.
Step-by-step explanation:
The most important action by the nurse in this scenario would be to b) Assess the client's dietary habits and nutritional intake.
During pregnancy, a woman needs only about 300 extra calories per day, on average, to support the growing fetus. It is important to assess the client's dietary habits and nutritional intake to ensure she is consuming the appropriate amount of calories and nutrients for a healthy pregnancy. Encouraging the client to increase caloric intake without assessing her current habits may lead to excessive weight gain, which can be detrimental to the baby's health.