We read with great interest the discussion that your Journal brought into clinical debate through an expert review by Cohen and Friedman and the answer by Zhang et al, whose seminal studies were the foundation for the welcomed recommendations by the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine on the new standards for the abnormality thresholds in the first and second stages of labor.

Our concern here regards what we are looking for in clinical practice and for future research.

We recently published an article on this topic in the Acta Obstetrica Gynecologica Scandinavica . In that article, we posed a completely different question concerning the labor curve assessment : Can a model be used to predict an individual patient’s future dilation when 1 or 2 cervical assessments in labor are available?

To model cervical dilation in nulliparous and multiparous women, we used data from spontaneous term labors that were attended only by midwives, without any iatrogenic interventions, such as sedation, peridural analgesia, amniotomy, and oxytocin. Cervical assessments were performed by midwives who used a 1-to-1 care protocol. Each patient had 2 to 5 cervical measurements. We adopted a combination of parsimonious (ie, with only 3 parameters to model the average shape of the labor curve), longitudinal, nonlinear mixed models that are used frequently to assess biologic growth patterns, as an alternative to polynomials or to smoothing algorithms.

Based on the curve that we obtained, we agree with Zhang et al ; we did not observe a deceleration phase, which could have been detected by the flexible model that we adopted (ie. a model that could account for an inflection point, if a deceleration phase occurred in the last stage of labor). As for the duration of the active phase of the first stage of labor (from 4 or 6 cm), it was exactly as long as the stage that was observed by the original work of Cohen and Friedman.

Our model and our successive observations allowed us to challenge and disprove the hypothesis that a single assessment of cervical dilation or consecutive assessments of the same laboring woman could predict her future dilation. We concluded with statistical evidence that “the rate of cervical dilation in spontaneous, naturally evolving labor was largely unpredictable, even when natural larger individual variability was excluded by clinical safety rules.”

Regarding clinical practice, a prudent assessment and intervention by acceleration is still indicated in cases with abnormal delay of cervical dilation; thanks to the new recommendations, these steps should not justify an aggressive clinical practice. In the past 50 years, the original intentions and actions that were meant to save fetal lives have turned from welcomed life-saving procedures into the major indications for cesarean deliveries.

As far as research for future clinical improvement, we should acknowledge that even recent evidence that has been produced by properly modeled curves is still “falling short” of evaluating the power systems that determine the length of labor in individual women. Baseline immune inflammatory balance, maternal stress and energy metabolism, placental metabolic conditions and fetal energy supply lines, the size and relative mechanical interaction between fetal body parts and the uterus, and myometrial contraction efficiency are not part of the diagnostic tools that are embedded in labor and delivery protocols.” As a matter of fact, the only recommended intervention is on myometrium contractions.

Indeed, in our opinion, the questions we should pose in research should not be “when and how” to accelerate labor but “why” the cervix (that little part of the uterus made of biologic polymers that can be transformed into jelly-like tissue in minutes) in that individual woman is not dilating as “expected” along averaged modeled curves. In the meantime, the quest for bedside diagnostic tools can be anticipated by clinical judgment: we can ask ourselves “Is the mother stressed, or are we caring for her to lower her stress hormones?” “Is she lacking energy, fasting more than overnight, or are we depriving her of the required energy to labor and for the fetus to stay active?” or “Is this baby 1 of the 30% of cases with a posterior head and trunk during the first stage, and are we keeping her bound to the bed instead of moving and walking around?” In the meantime, prudent diagnosis and action based on delayed progression is still mandatory based on the best evidence and tailored clinical interventions. We should be aware that these labor curves, both old and new, are based on mixed clinical conditions in which iatrogenic intervention is already the rule rather than the exception; that is to say, any time we accelerate labor, we act according to a curve already modeled on accelerated human labors.