Podcast Summary: "A BMI-Based Labor Curve?"

Dr. Chapa’s OBGYN Clinical Pearls
Date: November 9, 2025
Host: Dr. Chapa

Overview

This episode explores the question: Should we have BMI-specific labor curves in obstetric care? Dr. Chapa reviews a new study published in the American Journal of Obstetrics and Gynecology (the "Gray Journal") that investigates labor progression based on maternal Body Mass Index (BMI). Drawing on both evidence and clinical experience, the episode discusses the challenges and implications of applying "one size fits all" models in labor management—particularly regarding labor curves and fetal growth assessment.

Key Discussion Points & Insights

Universal Criteria in Medicine—A Double-Edged Sword

• Medicine often utilizes universal scales, which are mostly appropriate, but sometimes ill-fitting for specific populations (00:37).
  • “It’s interesting in medicine that we have universal scales or universal criteria for things...but there’s other criteria or other management guides that sometimes just don’t fit everybody.” (B, 00:37)

The Labor Curve—History & Current Use

• Friedman Curve: The historical gold standard for labor progression, once universally applied, is now mostly obsolete due to its rigidity (01:40).
• Current Labor Curve: Revised labor management now used; still, only one updated labor curve is applied to all patients, regardless of crucial differences like BMI.
• BMI is acknowledged to affect labor progression, but one standard curve remains the default (02:30).
• Dr. Chapa repeatedly mocks one-size-fits-all approaches: “One size fits all. Who are they kidding?” (C, recurring: e.g., 01:13, 02:27, 04:40, etc.)

The Issue with Universal Application

• Applying universal management to all can lead to problems—such as unnecessary interventions due to non-individualized criteria.
• Example: Using European-based fetal growth curves for genetically smaller populations (like Guatemalan or Peruvian patients) can also cause overdiagnosis of fetal growth restriction and lead to unnecessary interventions (04:44–07:09)
  • “Every mom ... their child looks growth restricted. Why? Because the original Hadlock formula was based on primarily Europeans who are a lot taller than tribal Guatemalans.” (B, 04:52)

New Research: Labor Progression by BMI

• Dr. Chapa reviews a just-released study: Characterizing Labor Progression and Duration According to Maternal Body Mass Index (from the Gray Journal, November 8, 2025) (02:30, 07:12).
• Main finding: “There is a direct linear deterioration in labor progress directly related to increasing levels of BMI.” (B, 07:12)

Statistical Language

• The study uses the phrase "positive monotonic pattern" to describe this correlation—Dr. Chapa lampoons the jargon but concurs with the finding (09:35).
  • “Why don’t we just say direct linear correlation? But no, they’ve got to go with a positive monotonic pattern.” (B, 09:31)

Why Not a BMI-Based Labor Curve?

• The rationale for a BMI-specific labor curve is strong, but logistical and practical issues remain:
  • Would need to be validated before adoption.
  • Application (discussing with patients) could be awkward or potentially offensive.
  • Currently, shared decision-making and individualized care are recommended instead (12:58, 17:00).

Practical Management Pearls

• Best practice is to allow more time for labor progression, especially in latent phase (4–6cm), for patients with higher BMI—consistent with ACOG and SMFM guidelines (07:12, 12:58).
  • “Please simply allow more time, especially in that early latent phase transition dilation stage of 4-6cm where things tend to get kind of stuck. Just be a little more gracious.” (B, 13:30)
• No separate, validated curves exist yet for different BMI classes, despite multiple calls in the literature.

Real-World Implications

• Using standardized curves for all leads to higher intervention rates (cesareans, operative deliveries) in individuals with larger BMI, with no benefit to maternal or neonatal outcomes (13:30–14:45).

  • “Using a standardized labor curve for all patients can lead to a higher rate of interventions in patients who are overweight and/or obese without having any benefit on maternal or neonatal outcome.” (B, quoting SMFM/consensus, 14:40)

• Shared decision-making and patience are key—especially in the absence of other indicators for intervention (16:00).

Other Considerations

• Options like titrated oral misoprostol (Canadian SOGC guidance) are discussed as alternative protocols, although not thoroughly studied in high BMI populations (15:20).

Notable Quotes & Memorable Moments

• On One-size-fits-all in Medicine:
  • “People are people... but there’s other criteria or other management guides that sometimes just don’t fit everybody.” (B, 00:37)
• Recurring Refrain:
  • “One size fits all. Who are they kidding?” (C, 01:13; 02:27; 04:40; etc.)
• On having a BMI-specific labor curve:
  • “Could you imagine telling the patient—no worries, if you were on the regular labor curve, we would have cut you hours ago. But honey, you’re on the obese labor curve. You’re doing just fine, girl!” (B, 13:55)
• Summary on Implications:
  • “Results suggest a potential need for the use of labor curves tailored to BMI... in order to avoid unnecessary cesarean deliveries.” (B, quoting study, 13:50)
• Clinical Take-home:
  • “Sometimes the best thing to do is allow. Now remember, before we start wrapping this up, I’m talking about generalities, okay?... Always be conservative and it will keep you honest and keep you safe.” (B, 18:30)

Important Timestamps

• Universal scales in medicine (00:37)
• Obstetric examples: labor curve & fetal growth (01:16–07:12)
• Review of new study (07:12–10:41)
• Practical management pearls & shared decision-making (12:58–14:45)
• Discussion of misoprostol protocols (15:20)
• Summary and clinical take-homes (16:00–18:30)

Key Takeaways

• Labor progression in high BMI patients is, on average, slower, particularly in the latent phase.
• Universal labor curves do not fit all; more individualized, patient-centered time frames are needed for those with high BMI.
• As of now, no validated, BMI-specific labor curves exist—pending future research.
• Allow more time before diagnosing labor arrest, especially in latent phase, to prevent unnecessary interventions.
• Realistic, empathetic communication and individualized care (“shared decision-making”) are essential.

Summary prepared for listeners seeking a concise, clinically relevant overview of Dr. Chapa’s exploration of BMI-based labor curves and current best practices in labor management.