Striae gravidarum (SG), or stretch marks of pregnancy, begin as erythematous streaks and eventually for hypopigmented atrophic bands. A recent study, published in the British Journal of Dermatology evaluated the molecular alterations that can potentially promote atrophy of SG. Researchers studied dermal type I collagen fibrils, which provide human skin with support. Skin samples of recently developed, erythematous abdominal SG were obtained from pregnant women. Second-harmonic generation imaging was performed using multiphoton microscopy to investigate the organization of collagen fibrils. Immunostaining assessed protein expression and localization of type I procollagen, the precursor of type I collagen fibrils. Real-time polymerase chain reaction helped determine gene expression levels. In control (hip) and stretched normal-appearing perilesional abdominal skin, dermal collagen fibrils were noted to be organized as tightly packed, interwoven bundles. In SG; however, collagen bundles were markedly separated, especially in the mid-to-deep dermis. The spaces separating these bundles contained loosely packed wavy collagen fibrils lacking organization. These disorganized fibrils persisted into the postpartum period and did not form densely packed bundles. Several large fibroblasts displaying type I procollagen expression were found close to the disorganized fibrils, suggesting that the fibrils are newly synthesized. Immunostaining and gene expression of type I procollagen were increased throughout the dermis of SG.

Early SG thus revealed considerable separation of collagen bundles and emergence of disorganized collagen fibrils that did not form bundles. This points to ineffective repair of collagen bundles disrupted by intense skin stretching. Persistent disruption of the collagenous extracellular matrix seems to enhance the formation and atrophy of SG.