What Causes Breast Pain in the Third Trimester of Pregnancy?

During the third trimester of pregnancy, many women experience breast tenderness or aching—a common and typically benign symptom rooted in profound hormonal and anatomical changes preparing the body for lactation.

This discomfort arises primarily from elevated levels of estrogen and progesterone, which stimulate mammary gland proliferation and ductal branching. Concurrently, rising prolactin levels promote lobuloalveolar development—the structural foundation for milk synthesis—while oxytocin primes myoepithelial cells for future milk ejection. These hormonal shifts cause increased blood flow, interstitial fluid accumulation, and tissue expansion within the breasts, often resulting in swelling, heaviness, sensitivity, or dull, persistent ache.

Additional contributing factors include rapid breast growth (particularly in first pregnancies), skin stretching, and mechanical strain from altered posture or increased breast mass. In most cases, symptoms are symmetrical and gradually intensify as gestation progresses, peaking near term.

While usually physiological, clinicians advise evaluation if tenderness is unilateral, associated with focal redness, warmth, fever, or a palpable mass—features that may suggest mastitis, cyst formation, or, rarely, malignancy. Likewise, sudden, severe, or sharp pain warrants assessment to exclude musculoskeletal strain, costochondritis, or referred cardiac or pulmonary pathology.

Conservative management includes well-fitted supportive maternity bras without underwire, warm compresses for comfort, gentle lymphatic massage, and avoidance of excessive stimulation. Symptoms typically resolve spontaneously after delivery or with the onset of lactation, though residual tenderness may persist during early breastfeeding as the mammary glands adapt to milk production demands.