Labor induction methods show similar effectiveness and differing safety profiles

A new review including over 100 clinical trials has found that no induction method was clearly effective than low-dose vaginal misoprostol, although some methods were less effective and safety profiles varied.

Induction of labor involves initiating labor using pharmaceutical or mechanical methods. It's common in obstetrics, particularly when there are health risks for the mother and baby or when pregnancies go beyond 42 weeks. Many induction methods exist, but the evidence behind them has previously been fragmented and unclear.

The review compared 13 different methods of induction using a statistical technique called network meta-analysis, which enables researchers to robustly combine data from multiple studies and compare interventions across different trials. Methods assessed included medication-based approaches (misoprostol, dinoprostone, oxytocin, nitric oxide donors), mechanical techniques (balloon catheters, osmotic dilators), and combination approaches (balloon with oxytocin or misoprostol; oxytocin with amniotomy).

In total, researchers included 106 randomised controlled trials involving more than 30,000 women who were at least 37 weeks pregnant and expecting a live baby. Most studies included women without a previous caesarean section, while evidence for women with a previous caesarean section remained limited. The review analysed and reported outcomes separately for women with and without a previous C-section.

Most methods are roughly similar in effectiveness at achieving birth. Misoprostol, which can be applied directly to the vagina or taken orally, was widely used in the studies and is common in clinical practice. Low-dose vaginal misoprostol was the most common comparator in the included trials, so served as a practical benchmark for comparison.

The findings showed no clear evidence that any induction method outperformed low-dose vaginal misoprostol in achieving vaginal delivery within 24 hours, reducing caesarean section due to concerns about fetal well-being, or preventing perinatal death.

"Induction of labor is extremely common, and having the right method matters for both mother and baby," said Dr Ioannis Gallos, medical officer at HRP and the World Health Organization and lead clinical author of the review. "What this review shows is that while many approaches are similarly effective, some are clearly safer in certain circumstances, especially for women without a previous caesarean section. This evidence helps clinicians choose the right method for the right patient, based on solid data rather than habit or preference."

Whilst the overall evidence shows no method clearly outperformed low-dose vaginal misoprostol, some induction methods ranked higher in the network analysis. Oxytocin with amniotomy was the most successful method for achieving vaginal birth within 24 hours, while balloon catheter plus low-dose misoprostol offered the most reliable improvement; methods such as nitric oxide donors, osmotic dilators and balloon catheters substantially reduced the risk of uterine hyperstimulation that can distress the baby but achieved lower 24‑hour success, and overall differences in caesarean section due to fetal concerns were small, with balloon plus oxytocin being the most beneficial.

Safety profiles differed between the methods, especially for uterine hyperstimulation that can distress the baby, fetal distress, and risk of uterine rupture in women without previous C-section.

The authors stress that whilst all methods of induction of labor are valid, the safety of mechanical methods should be the main takeaway from this review. 

Mechanical methods may not be more effective than some other induction methods. However, mechanical methods are quite safe, particularly for the baby's well-being and for avoiding uterine rupture. Some - such as balloon catheters - are widely available and inexpensive. Cost, availability, and acceptability influence guideline recommendations, especially in low-resource settings."

Siwanon Rattanakanokchai, first author of the review

No methods were deemed so unsafe that they should be abandoned, though the authors urge that success profiles did vary for each outcome and clinical context matters, particularly in women with previous C-sections and in settings with limited resources.

"Despite how common induction is, the evidence base remains surprisingly thin for women with previous caesarean sections," said senior author Pisake Lumbiganon. "Whilst the findings are important in informing guidelines about which methods are safest and most efficient, they've also highlighted a critical research gap with direct implications for future guidelines."