A validated calculator to estimate risk of cesarean after an induction of labor with an unfavorable cervix

Lisa D. Levine, Katheryne L. Downes, Samuel Parry, Michal A. Elovitz, Mary D. Sammel, Sindhu K. Srinivas

Research output: Contribution to journalArticlepeer-review

70 Scopus citations


Background: Induction of labor occurs in >20% of pregnancies, which equates to approximately 1 million women undergoing an induction in the United States annually. Regardless of how common inductions are, our ability to predict induction success is limited. Although multiple risk factors for a failed induction have been identified, risk factors alone are not enough to quantify an actual risk of cesarean for an individual woman undergoing a cesarean. Objective: The objective of this study was to derive and validate a prediction model for cesarean after induction with an unfavorable cervix and to create a Web-based calculator to assist in patient counseling. Study Design: Derivation and validation of a prediction model for cesarean delivery after induction was performed as part of a planned secondary analysis of a large randomized trial. A predictive model for cesarean delivery was derived using multivariable logistic regression from a large randomized trial on induction methods (n = 491) that took place from 2013 through 2015 at an academic institution. Full-term (≥37 weeks) women carrying a singleton gestation with intact membranes and an unfavorable cervix (Bishop score ≤6 and dilation ≤2 cm) undergoing an induction were included in this trial. Both nulliparous and multiparous women were included. Women with a prior cesarean were excluded. Refinement of the prediction model was performed using an observational cohort of women from the same institution who underwent an induction (n = 364) during the trial period. An external validation was performed utilizing a publicly available database (Consortium for Safe Labor) that includes information for >200,000 deliveries from 19 hospitals across the United States from 2002 through 2008. After applying the same inclusion and exclusion criteria utilized in the derivation cohort, a total of 8466 women remained for analysis. The discriminative power of each model was assessed using a bootstrap, bias-corrected area under the curve. Results: The cesarean delivery rates in the derivation and external validation groups were: 27.7% (n = 136/491) and 26.4% (n = 2235/8466). In multivariable modeling, nulliparity, gestation age ≥40 weeks, body mass index at delivery, modified Bishop score, and height were significantly associated with cesarean. A nomogram and calculator were created and found to have an area under the curve in the external validation cohort of 0.73 (95% confidence interval, 0.72–0.74). Conclusion: A nomogram and user-friendly Web-based calculator that incorporates 5 variables known at the start of induction has been developed and validated. It can be found at: http://www.uphs.upenn.edu/obgyn/labor-induction-calculator/. This calculator can be used to augment patient counseling for women undergoing an induction with an unfavorable cervix.

Original languageEnglish
Pages (from-to)254.e1-254.e7
JournalAmerican Journal of Obstetrics and Gynecology
Issue number2
StatePublished - Feb 2018
Externally publishedYes


  • Bishop score
  • calculator
  • cesarean
  • failed induction
  • induction of labor
  • unfavorable cervix


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