When Does Rectus Diastasis Worsen the Most? A Pregnancy-Order Analysis of Midline Fascial Failure.

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backgroundDiastasis of the rectus abdominis muscles (DRA) is common after pregnancy, yet little is known about its sequential progression across multiple gestations. While multiparity is a recognized risk factor for greater diastasis severity, it remains unclear whether midline widening increases linearly with each pregnancy or follows a nonlinear biomechanical pattern with specific points of maximal fascial failure.

objectivesTo evaluate how maximal inter-rectus distance (IRDmax) changes after each pregnancy in women who have completed childbearing, and to determine whether distinct worsening patterns can be identified.

methodsA retrospective cohort study was conducted on 117 postpartum women seeking abdominal wall reconstruction. Radiologic measurements of IRDmax (ultrasound, CT, or MRI) obtained after each pregnancy were collected and parity-matched. The primary endpoint was the within-patient sequential change in IRDmax across gestations. Polynomial and segmented regression models were used to detect inflection points, nonlinear trajectories, and plateau behavior.

resultsThe greatest mean increase in IRDmax occurred between the first and second pregnancies ( + 1.9 cm; +59.4%), representing the primary inflection point in 88.1% of patients. Subsequent pregnancies showed significantly smaller widening increments (0.4-0.7 cm), indicating a relative post-second-pregnancy plateau. A minority (22.2%) demonstrated late or progressive worsening beyond the third pregnancy, associated with higher mechanical load factors such as twin gestations, elevated fetal birth weight, and excessive maternal gestational weight gain-suggesting inter-individual variability in collagen quality and abdominal wall compliance.

conclusionsDRA progression does not follow a linear cumulative model. For most women, the second pregnancy represents the major biomechanical stress event responsible for the greatest fascial deterioration, after which midline widening tends to stabilize. However, patients exposed to high intra-abdominal pressure loads may continue to worsen in later pregnancies. Recognition of these trajectory patterns is valuable for surgical counseling, timing of abdominal wall repair, and risk assessment for recurrence. LEVEL OF EVIDENCE IV: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors   www.springer.com/00266 .