This is a retrospective study led by The Sixth Affiliated Hospital, Sun Yat-sen University, focusing on newborns diagnosed with necrotizing enterocolitis (NEC)-a serious gastrointestinal disease that threatens newborns' lives-between January 2023 and June 2025.

Purpose of the study: NEC can lead to severe conditions like bowel perforation or even death, and it's hard for doctors to spot high-risk babies early with current tools. This study aims to analyze the babies' clinical information (e.g., birth weight, symptoms like belly swelling or bloody stools), blood test results (e.g., lactate levels, white blood cell counts), and organ function scores (nSOFA scores) to find indicators that can predict whether NEC will get worse or cause death.

Questions the study tries to answer: Can combining metabolic indicators (like lactate), blood test parameters, and organ function scores better predict if a newborn with NEC will develop perforated NEC (a more severe form where the bowel has holes) or die during hospitalization? Are these combined indicators more reliable than single indicators alone? Study hypothesis: We guess that integrating metabolic markers (such as lactate), blood routine parameters, and nSOFA scores will be more accurate than using any single indicator to predict the progression of NEC and the risk of death in affected newborns.

1. Study Rationale Necrotizing Enterocolitis (NEC) is a life-threatening gastrointestinal disorder primarily affecting very low birth weight (VLBW) neonates (incidence: 5-12%). Around 20-40% of cases progress to severe disease requiring surgery, and survivors often face long-term complications (e.g., short-bowel syndrome, neurodevelopmental impairments). Despite advances in neonatal care, early identification of high-risk patients remains challenging due to nonspecific clinical/radiographic signs and insufficiently sensitive/specific conventional biomarkers.

   NEC pathophysiology involves intestinal ischemia-reperfusion injury, excessive immune activation, and microbial dysbiosis. Serum lactate (a marker of hypoperfusion/anaerobic metabolism) correlates with NEC severity but lacks specificity; peripheral blood cell (CBC) indices are accessible but understudied in combination with lactate. The Neonatal Sequential Organ Failure Assessment (nSOFA) score predicts overall NEC mortality but fails to stratify risk for perforated NEC (PNEC), a high-risk subtype. This study aims to address gaps by integrating metabolic (lactate), hematologic (CBC), and organ dysfunction (nSOFA) metrics for NEC prognosis.

2. Study Design and Conduct This is a retrospective cohort study conducted at the Sixth Affiliated Hospital, Sun Yat-sen University, approved by the institutional ethics committee and compliant with the Helsinki Declaration. The study period is January 1, 2023-June 30, 2025; eligible participants are identified via retrospective review of electronic medical records (EMRs), with data extracted in a structured manner.

3. Data Collection

   Structured EMR extraction captures key variables:

   Neonatal history: Sex, gestational age, birth weight, birth asphyxia (Apgar scores), small for gestational age (SGA) status, preterm complications (e.g., patent ductus arteriosus [PDA], respiratory distress syndrome [RDS]), feeding pattern, mechanical ventilation use.

   Maternal history: Delivery mode, chorioamnionitis, premature rupture of membranes.

   NEC-related parameters: Bell's staging, clinical manifestations (e.g., abdominal distension, pneumoperitoneum), complications (sepsis, shock), therapeutic interventions (surgery), in-hospital mortality.

   Laboratory/organ dysfunction indicators: Serum lactate (at NEC onset), CBC parameters (WBC, neutrophils, lymphocytes, platelets) and derived inflammatory indices, nSOFA score (at NEC onset).

4. Statistical Analysis

   Analyses use SPSS 26.0 and GraphPad Prism 9.0:

   Data expression: Normally distributed variables (mean ± SD), skewed variables (median [IQR]), categorical variables (frequency %).

   Intergroup comparisons: Chi-square/Fisher's exact test (categorical), t-test/Mann-Whitney U test (continuous).

   Multivariate logistic regression: Includes variables with p<0.05 from univariate analysis to identify independent predictors.

   Mediation analysis (PROCESS macro 4.1, 1000 bootstraps): Decomposes total effects into direct/indirect paths.

   ROC curve analysis: Evaluates predictive performance of single/combined biomarkers (AUC as metric). All tests are two-tailed; p<0.05 is significant.

5. Study Objectives Primary: Identify indicators predicting NEC progression (PNEC) and in-hospital mortality via analysis of clinical, metabolic, and laboratory data.

   Secondary: Explore integrated biomarkers for NEC severity stratification (e.g., Bell's staging, surgical need) to optimize clinical decision-making.

6. Participant Protection All data are de-identified before analysis and stored in a password-protected database (accessible only to the study team). Informed consent is obtained from participants' legal representatives, who are informed of the right to withdraw at any time without penalty.

Inclusion Criteria:

• (1) Diagnosis of NEC and having undergone surgical treatment, confirmed by clinical manifestations (e.g., abdominal distension, bloody stools), radiological evidence (pneumatosis intestinalis, portal venous gas, or pneumoperitoneum), and pathological examination in accordance with established guidelines; (2) Availability of complete medical records for data extraction.

Exclusion Criteria:

• (1) Congenital gastrointestinal malformations (e.g., intestinal atresia, Hirschsprung's disease) or spontaneous intestinal perforation; (2) Hereditary metabolic disorders; (3) Incomplete clinical data or refusal of participation.

In this study, a retrospective analysis was conducted on 400 enrolled neonates with necrotizing enterocolitis (NEC), with data collected at The Sixth Affiliated Hospital, Sun Yat-sen University from January 2023 to June 2025.