Is cervical dilation unpredictable?

No one really believes the Friedman Curve represents timing of cervical dilation anymore.   Modern researchers have used more sophisticated techniques to identify problems with the Friedman Curve, generally about the slope of the line which represents the speed or progress of dilation. What remains from the Friedman Curve is the idea that labor has a line that can represent the normal process of dilation.

This line becomes the basis of judgement of normality of labor. In some places the labor progress is charted in a partograph to allow visual comparison of the progress to the line. Decisions to intervene are made based on deviation from this line.

So what happens if this line doesn’t exist?

I ask because researchers in Italy found unexpected levels of variability in the natural progression of cervical dilation (the “line”). The variability did not only exist prior to 6cm dilation, but also after. In fact, the researchers couldn’t find any correlation in the speed of dilation between those who dilated fastest and those who dilated slowest.  In short, the progress of spontaneous, naturally progressing labor was unpredictable.

So I ask again, what happens if this line doesn’t exist?

A few things to remember as you consider this:

  • These were spontaneous, naturally progressing labors. In cases of induction a measure of treatment effect would be needed to ensure safety on the fast side (generally the number of contractions in 10 minutes), and meeting the goal of the intervention on the slow side (generally cervical dilation). As one of my midwife mentors put it, “You don’t induce unless you know she needs to be induced. And if you know she needs to be induced, you want that induction progressing.”
  • This was one study with 328 women. While it is tempting to say this study “undoes” everything researchers said previously about cervical dilation it is most accurate to say this study provides more information that should be understood within the context of everything researchers have said previously about cervical dilation. Every study uses different measures, methods of examination, etc.
  • As researchers continue to explore the variation in naturally progressing labor we are likely to find the things that are hidden to us now.

Surely at some point everyone agrees slow progress in labor indicates something isn’t working properly, but the question is where would that point be?

What variation in cervical change is “normal, healthy” variation among women, and what variation is due to other things?

What might those “other things” be?