• Hautakangas et al. (BJOG, 2022) investigated the impact of severe obesity (BMI ≥35 kg/m2) on uterine contractile activity 

• Exploratory, blinded analysis of a prospective cohort from a previous RCT 
• Primary RCT compared intrauterine and external tocodynamometries and labor outcomes 
• Population 
  • Singleton pregnancies 
  • ≥ 37 weeks 
  • Cephalic presentation 
  • Intrauterine tocodynamometry during labor 
• Exposures 
  • Severe obesity: BMI ≥35 kg/m²  
• Primary outcome 
  • Uterine contractile activity 
    • Assessed as intrauterine pressure, frequency of contractions and basal tonus of uterine muscle 
• Secondary outcomes 
  • Use of oxytocin 
  • Labor outcomes 

• 686 participants 
  • BMI ≥35 kg/m²: 84 participants 
• Participants with obesity reached intrauterine pressure ≥200 MVUs during the first stage of labor more often than those with BMI <35 kg/m² 
  • BMI ≥35 kg/m²: 62% 
  • BMI <35 kg/m²: 49% 
  • OR 1.67 (95% CI, 1.05 to 2.67) 
• Participants with obesity also had a higher basal tone of uterine muscle 
• Women with obesity without a previous vaginal delivery  
  • Were more likely to fail to reach the active stage of labor  
    • OR 2.36 (95% CI, 2.39 to 4.37); P=0.005 
  • Were more likely to require cesarean 
    • OR 1.88 (95% CI, 1.08 to 3.27); P=0.024 
• If a parturient had had previous vaginal delivery 
  • Obesity did not influence uterine activity 
  • There was no increased risk for caesarean 
• Doses and total oxytocin amounts did not significantly differ between BMI groups 

• Women with obesity were less likely to reach the active stage of labor and were more likely to require cesarean 
• However, these outcomes are probably not due to decreased uterine contractile activity as uterine contractility was increased vs leaner participants 
• The authors state 

The uterine contractile activity of obese parturients is equal to or even greater than that of leaner parturients, but obese parturients less often achieve vaginal delivery 

However, if the active stage of labour is reached, obese parturients have labours that are as straightforward as those among leaner parturients 

Impact of obesity on uterine contractile activity during labour: a blinded analysis of a randomised controlled trial cohort 

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