Perioperative Hemoglobin Decline After Deep Endometriosis Surgery: Association with Surgery Duration and Exploratory Analyses of Operative Extent

Background/Objectives: Deep endometriosis surgery may require bowel and multiorgan procedures. We quantified the frequency of a hemoglobin decline of at least 3 g/dL and examined associations with surgery duration and clinically recognizable measures of operative extent. Methods: This single-center retrospective cohort included the first eligible surgery per patient from 2020 through 2025. Hemoglobin decline was the last preoperative value within 7 days before surgery minus the lowest recorded postoperative value through day 3. Multivariable regression examined a decline of at least 3 g/dL and continuous decline; secondary analyses assessed operative extent, models excluding preoperative hemoglobin, and missing data. Results: Among 424 patients, 416 (98.1%) had paired measurements; 156/416 (37.5%) met the primary outcome. Each additional surgical hour was associated with higher odds (odds ratio [OR], 1.61; 95% confidence interval [CI], 1.35–1.91); the estimate was similar without preoperative hemoglobin (OR, 1.50; 95% CI, 1.28–1.76). Continuous decline was 0.20 g/dL greater per hour (95% CI, 0.13–0.26). The lowest recorded postoperative value occurred on days 2–3 in 242/421 patients (57.5%); sampling was not standardized. Among 379 patients with available resection-multiplicity data, exploratory outcome rates were 14.5%, 38.3%, and 54.9% after no, one, and multiple full-thickness bowel resections, respectively. Conclusions: A hemoglobin decline of at least 3 g/dL occurred after 37.5% of surgeries. Longer duration was associated with greater decline; exploratory analyses suggested gradients with operative extent. Their monitoring value requires prospective evaluation. Preoperative anemia remains relevant because the same decline produces a lower postoperative concentration.