Iatrogenic Norms: How Fast Do First-Time Mothers Beginning Labor Spontaneously Actually Dilate?
Iatrogenic (adjective): induced in a patient by a health care provider’s activity, manner, or therapy. An iatrogenic disorder is caused by medical personnel or procedures or develops through exposure to a health care facility.
Iatrogenic norm: a defined range of normal values for a biological process that, rather than describing actual normal physiology, instead measures the consequences of a health care provider’s beliefs, actions, or therapies or the effects of exposure to a health care facility.
Clinicians today base labor management on norms for cervical dilation rate in active phase labor (assumed to begin somewhere between 3 and 5 cm dilation in women contracting regularly) derived from research conducted decades ago by Friedman and colleagues (the famous “Friedman curve”). According to this research, in first-time mothers, the slowest 10%, an arbitrary cutoff for abnormally slow progress, dilate at a rate of 1.2 cm per hour or less. This norm has been enshrined in the “action lines” of the graphs of “dilation versus time” routinely used to manage labor. The “action” taken when women fail to progress at this minimal rate is administration of intravenous oxytocin to strengthen contractions, and such women are at high risk for cesarean surgery for labor dystocia. If this criterion is overly stringent, women with normally progressing labors will be subject to potentially harmful treatment and surgical delivery unnecessarily.
Concern over this possibility led a group of investigators to conduct a systematic review of studies analyzing active labor duration, progress rate, or both in active first-stage labor in first-time mothers, and the lead author, Jeremy Neal, presented the results at the recent Normal Labour & Birth International Research Conference. Neal began his talk with a look at the body of evidence that gave rise to this concern. I won’t bore you with the details, but suffice it to say that studies using Friedman’s norms for progress diagnose anywhere from one-quarter to one-half or more of first-time moms as requiring treatment for abnormally slow progress. If progress is abnormal in that many women, then something is wrong with the definition of normal, or, as Neal put it:
Either many nulliparous women are admitted prior to progressive (active) labor yet held to dilation expectations of “active‟ labor and/or common expectations of active labor dilation rates (e.g. 1 cm/hr) are unrealistically fast.
The group’s review pooled data from 25 studies encompassing thousands of low-risk first-time mothers with spontaneous labor onset at 36 weeks of pregnancy or more. It found that contrary to Friedman, 1.2 cm was actually the mean rate of dilation, not the rate in the slowest 10%, and the limit for the threshold of slowest acceptable progress rate fell at 0.6 cm, half that rate. (This, by the way, is not a physiologic norm because studies included women with epidurals and labor augmentation, and since all data came from hospital studies, laboring women would have been subject to policies that could affect progress rate such as confinement to bed. That being said, the review found that epidural use did not change results.)
Neal then added that active labor is assumed to progress at a constant rate, but some data suggest that rate of progress may be slower at the beginning of active phase and accelerate as it continues. In other words, the action “line” is another iatrogenic norm because it should be an action “curve.” If this is true, using an action line would put even more women progressing normally in early active phase in jeopardy of the “dystocia” diagnosis and all that follows.
Neal concluded with: “Revision of existing ‘active’ labor expectations and/or revision of criteria used to prospectively identify active labor onset is warranted and such efforts should supersede efforts to ‘change’ labor to fit existing expectations.” “From his mouth to God’s ears,” as they say—or at least to the ears of obstetricians.
Nevertheless, while revising norms to match reality would take a big step in the right direction, I would argue it doesn’t go nearly far enough because it still sticks us with the assumption that active first-stage dilation progresses smoothly. Anyone who has spent time with laboring women knows that this is often not the case. Neat graphical lines (or curves) come from averaging many highly variable individual labors, so the very expectation of how labors progress, at whatever pace, is itself an iatrogenic norm.
Moreover, the published review points out that both the old and the proposed new threshold for “abnormal” are statistically derived (e.g. two standard deviations beyond the mean). No study links a cut point for “abnormally slow” with an increase in perinatal morbidity, but averting adverse outcomes should form the basis for intervening medically because of the risks of intervention. In fact, even if a study tried to establish an outcome-based threshold, it would be hard to determine whether the increase was due to labor duration per se or to the interventions used to treat slow labor. So we have yet another iatrogenic norm, this one having to do with a definition of “abnormal” with no clinical significance.
In short, forcing labor to conform to artificial, arbitrary guidelines does more harm than good. A simplistic cookbook approach to the knotty problem of labor dystocia has obvious appeal, but what is truly needed to achieve the best outcomes with the least use of medical intervention is thoughtful evaluation, individualized care, and above all, patience so long as mother and fetus are tolerating labor. Labor graphs and action lines do no more than exemplify H. L. Mencken’s truism, “For every complex problem there is a solution that is simple, neat—and wrong.”