Amniotomy or oxytocin for induction of labor. Re-analysis of a randomized controlled trial

Acta Obstet Gynecol Scand. 1988;67(8):731-5. doi: 10.3109/00016349809004298.


A recently reported "prospective, randomized study into amniotomy and oxytocin as induction methods in a total unselected population" was examined for selection bias and bias after entry into the study. The null hypothesis that clinical attitudes to amniotomy as a means for inducing labor had no influence on the decision to enter women into the trial and allocate them to either amniotomy or oxytocin was rejected at p less than 0.00025. Clinical attitudes were further found to statistically significantly influence the prescribed assessments 4 h after entry into the trial and the selection of the second intervention that was required in the absence of acceptable progress (p less than 0.0005). Bias at the time of this prescribed assessment was large enough to result in an inverse relationship between "acceptable progress within 4 hours" and "delivery within 24 hours" after induction. A subanalysis of the nulliparae entered into the trial further substantiated both bias at entry and bias in following the prescribed protocol. As hypothesized, these biases reached a greater statistical significance in nulliparous than in parous women. The likelihood that all of these observations would be encountered in a truly randomized study of this size can be estimated to be less than one in a billion (or p less than 0.000,000,000,000,1). The study, therefore, provides a classical example of the dangers of non-blind allocation to different treatment groups in clinical trials. It is further concluded that no randomized controlled studies between amniotomy and oxytocin in a "total unselected population" are available.

Publication types

  • Clinical Trial

MeSH terms

  • Amnion / surgery*
  • Clinical Trials as Topic
  • Female
  • Humans
  • Labor, Induced* / methods*
  • Oxytocin / therapeutic use*
  • Parity
  • Pregnancy
  • Random Allocation


  • Oxytocin