The Friedman Curve: An Obsolete Approach to Labor Assessment

Journal Watch. 2003;2(2) 



The Friedman curve, the gold standard for rates of cervical dilation and fetal descent during active labor, was developed almost 50 years ago. To define a modern curve for normal labor, these researchers evaluated data on 1329 nulliparous, full-term women with spontaneous labors and vertex presentations who gave birth to singletons of normal birth weight from 1992 to 1996.

Dilation in the active phase was much slower on the modern curve than on the Friedman curve (mean time from 4 cm to complete dilation, 5.5 vs. 2.5 hours). Among the current study's patients, labor lasting more than 2 hours without apparent change was not uncommon before 7 cm of dilation. Friedman described 3 stages in the active phase: acceleration, maximal slope, and deceleration. No deceleration stage was noted in the contemporary curve.


The Friedman curve for normal active labor is one of the first pieces of knowledge that most obstetric students acquire. Comparison of Friedman's population with the current study's population shows marked differences: Anesthesia and augmentation are much more common now than in the past, and birth and maternal weights have increased substantially. The authors suggest that in addition to the discrepancies between the 2 groups of parturients, methodologic differences also might explain the differences between the curves. For example, Friedman actually plotted 500 individual curves and then synthesized them into 1 curve, whereas the current researchers used repeated-measures analysis with 10th-order polynomial function.

The authors conclude that the Friedman curve likely represents an ideal, rather than an average, curve. Although this study has limitations (e.g., assessment of cervical dilation is somewhat subjective), practitioners who base their diagnoses of protraction and arrest solely on the Friedman curve might need to reconsider their approach to labor assessment.

— Ann J. Davis, MD


Zhang J et al. Reassessing the labor curve in nulliparous women. Am J Obstet Gynecol 2002 Oct; 187:824-8.

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