Which sign is a potential indication of thrombophlebitis in a client on oral contraceptives?

Pain in the calf is a significant indicator of thrombophlebitis, especially in clients taking oral contraceptives. This condition arises from inflammation of the vein, typically in the legs, which can lead to a blood clot. One of the classic signs of thrombophlebitis is localized pain, which can manifest as a cramp or tenderness in the calf area.

Oral contraceptives can increase the risk of thrombosis due to their effects on blood clotting factors and vascular health. Consequently, individuals on these medications need to be vigilant in observing symptoms such as calf pain, as it may indicate a serious condition like deep vein thrombosis, which can progress to more severe complications such as pulmonary embolism.

The other choices, while they may indicate various health concerns, do not specifically suggest thrombophlebitis. Swollen, tender breasts can relate more to hormonal changes, frequent headaches can occur for many reasons including hormonal fluctuations or tension, and unexplained weight loss could indicate a number of health issues, but none are direct indications of thrombophlebitis. Thus, the presence of calf pain stands out as the most relevant symptom in this context.