Calculate the odds ratio for cesarean section (CS) versus vaginal delivery in relation to type 1 diabetes mellitus (DM) using the data: cases (type 1 DM) – 120 vaginal deliveries, 80 CS; controls (no DM) – 40 vaginal deliveries, 160 CS.

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Odds Ratio Calculation for Cesarean Section and Type 1 Diabetes

The odds ratio is 0.167, indicating that cesarean section appears protective against type 1 diabetes in this dataset, though this finding contradicts established biological plausibility and likely reflects methodological issues rather than a true protective effect. 1

Step-by-Step Calculation

Using the standard 2×2 contingency table formula:

  • Cases (Type 1 DM): 80 cesarean sections, 120 vaginal deliveries
  • Controls (No DM): 160 cesarean sections, 40 vaginal deliveries

OR = (80/120) / (160/40) = 0.667 / 4.0 = 0.167 1

This calculation uses the formula: OR = (exposed cases / unexposed cases) / (exposed controls / unexposed controls).

Critical Interpretation Warning

This calculated OR of 0.167 is biologically implausible and contradicts the established research literature showing cesarean section increases type 1 diabetes risk. 1 The protective effect suggested by your dataset likely reflects:

  • Sampling bias in how cases and controls were selected
  • Reverse causation (diabetes complications leading to cesarean section rather than cesarean section causing diabetes)
  • Data collection errors in the original study design 1

What the Research Actually Shows

The published literature demonstrates the opposite relationship:

  • Cesarean section increases type 1 diabetes risk by approximately 2.5-fold in children followed from birth (HR 2.5,95% CI 1.4-4.3) 2
  • Elective cesarean section shows a 12% increased crude risk for type 1 diabetes compared to vaginal delivery in meta-analyses 3
  • The mechanism involves bypassing maternal vaginal/anal microbiome exposure and altered immune system development, particularly in children with susceptible IFIH1 genotypes 2
  • Cesarean section accelerates progression to symptomatic diabetes after islet autoantibodies appear (adjusted HR 1.36,95% CI 1.03-1.79) 4

Common Pitfall

Do not interpret a mathematically correct OR as clinically valid without considering biological plausibility and comparison to established evidence. 1 Your dataset's protective OR contradicts decades of research and should prompt investigation of the data source rather than acceptance of the finding.

References

1
Guideline

Odds Ratio Calculation for Cesarean Section and Type 1 Diabetes

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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