Final answer:
In the first trimester, a client should expect to experience morning sickness, which is characterized by nausea and vomiting throughout the day.
Step-by-step explanation:
The nurse should instruct the client to expect morning sickness in the first trimester. Morning sickness includes symptoms of nausea and vomiting which although typically occur in the morning, can happen at any time of the day. Unlike the other options provided, such as quickening (feeling the baby's movements), Braxton Hicks contractions (false labor), and lightening (the baby moving down into the pelvis), morning sickness is common and often one of the very first signs of pregnancy during the initial weeks, sometimes even before a missed period.