Which symptom experienced by a pregnant client requires immediate cessation of exercise?

The symptom that necessitates an immediate cessation of exercise for a pregnant client is abdominal pain. Abdominal pain during pregnancy can be a sign of several serious conditions, including potential complications like ectopic pregnancy, placental abruption, or preterm labor. It indicates that something may be wrong, requiring immediate medical evaluation.

While fatigue, nausea, and dizziness can also be concerning symptoms, they do not typically pose the same level of immediate risk as abdominal pain. It's important for any pregnant client experiencing sudden or severe abdominal pain during exercise to stop immediately and seek medical advice to ensure their safety and well-being, as well as that of the fetus.