Objective: To objectively describe changes to nipple skin and classify signs of nipple trauma in breastfeeding women during postpartum week 1.

Methods: This study was conducted in two phases. Phase 1 was an observational prospective study of breastfeeding mothers in which data were obtained from photographs and digital images of nipple skin and analyzed to anatomically classify signs of nipple trauma. In Phase 2, the reliability of signs identified in Phase 1 was verified with the cooperation of eight clinical midwives.

Results: A total of 776 images of 50 breastfeeding mothers were obtained daily. The signs of nipple trauma included erythema, swelling, blistering, fissure, and scabbing. Purpura and peeling were identified only with photographic image analysis. Scabbing and blistering were classified as damage to the dermis, and erythema and swelling as damage to the epidermis, based on anatomical evidence and the mothers' subjective experiences of pain intensity. Erythema and swelling were observed from day 0, with erythema most frequently observed. For inter-rater reliability of the five signs of nipple trauma, Kendall's coefficient of concordance ranged from 0.46 (moderate) to 0.85 (almost perfect). Reliability was high for fissure, substantial for blistering and scabbing, and moderate for erythema and swelling.

Conclusions: Image analysis revealed five signs of nipple trauma. Erythema and swelling were the most frequently observed signs during postpartum week 1. However, the agreement rate was lower than that for other signs, suggesting the possibility of conflicting interpretations in clinical evaluation.