The curve, depicted in graph form, shows the progress of labor where cervical dilation and fetal descent are plotted on a vertical axis. Along the horizontal axis is the element of time. Like a mathematical graph, the Friedman’s curve is divided into stages and phases of labor. When there is a disparity in the slope of the curves, labor is termed dysfunctional.
Studies done during the first decade of this century demonstrate that the parameters to determine if labor is progressing need to be expanded. The reasons for expansion may be the increase in medical technology, specifically the rise in epidural anesthesia and subsequent inactivity during labor which can prolong the labor. A study published in 2004 in the Journal of Obstetrics, Gynecology and Neonatal Nursing (Cesario, S. Reevaluation of Friedman’s Labor Curve: a pilot study. 2004 Nov-Dec; 33(6):713-22) suggested “With the availability of technology to assess maternal and fetal well-being, labor should be allowed to progress past the rigid 2-hour time limit for the second stage of labor artificially imposed on women in some childbirth settings. More emphasis should be placed on the nursing assessment techniques used to reassure the family and health care practitioners that labor is progressing safely and the nursing interventions that may have an impact on the length of each stage of labor.”
From an article on Birthsource.com, current definitions of labor protraction and arrest may be too stringent, Dr. Jun Zhang of the National Institute of Child Health and Human Development, in Bethesda, Maryland said at the 2002 annual meeting of the Society for Maternal-Fetal Medicine. "And the long-accepted Friedman curve may not be an accurate description of normal labor progression, according to a new analysis of data from 1,329 nulliparous women aged 18-34 undergoing singleton, vertex presentation deliveries following spontaneous labor," said Dr. Zhang.
Based on the speed of overall labor progression and current cervical dilation, Dr. Zhang and his colleagues calculated the expected traverse time for the cervix to reach the next centimeter and the expected rate of cervical dilation at each phase of labor. "Our curve is very different," Dr. Zhang said, pointing out that on his curve the average was 5.5 hours for progression from 4 cm to 10 cm, compared with 2.5 hours on the Friedman curve.
"We also didn't see a deceleration phase," he said, noting that in 1978 Friedman modified his curve, but the distinctive sharp upturn remained, as did the deceleration phase. "Our data suggest that most women enter active labor at different times, mostly between 3 cm and 5 cm dilation, and even in the active phase the speed of progression varies from person to person," he further explained. The median time for cervical dilation to progress from 4 cm to 5 cm in the present study is 1.7 hours. And for fetal descent, it could take 3 hours to progress from station +1 to +2, and an additional half hour from station +2 to delivery, he added. "Therefore, the definition of protracted descent or arrested descent appears to be too stringent in current practice," according to Dr. Zhang. Read more…
Dr. Zhang again calls into question the use of the Friedman’s curve in 2006 and refines insight into labor progress, the diagnostic criteria for labor protraction and arrest disorders.
And in December of 2010, Zhang again questions existing practice by the study gathering data from over 62,000 birthing women. Their conclusions were as follows:
"Judging whether a woman is having labor protraction and arrest should not be based on a research definition of an average starting point or average duration of labor," the researchers write. Instead, an upper limit of what is considered 'normal labor' should be used in patient management. "As long as the labor is within a normal range and other maternal and fetal conditions are reassuring, a woman should be allowed to continue the labor process."
The differences they observed could be due to the fact that women giving birth are older and heavier, on average, than they were when Dr. Friedman's labor curves were developed, the researchers note; "these factors are known to affect labor progress and duration."
Therefore, based on several large studies and over a decade of research, the evidence says that the rate of cervical dilation accelerated after 6 cm, and progress from 4 cm to 6 cm was far slower than previously described. Allowing labor to continue for a longer period before 6 cm of cervical dilation may reduce the rate of intrapartum and subsequent repeat cesarean deliveries in the United States. Clinging to the original Friedman’s Curve may “cause” an increase in cesarean section.
"The Length of Active Labor in Normal Pregnancies," by Leah I. Alberts,CNM,PhD: Melissa Schiff, MD; and Julie G. Gorwoda, CNM,MSN. Obsterics & Gynecology. 87(3):355.359, March 1996.
“Contemporary patterns of spontaneous labor with normal neonatal outcomes” by Jun Zhang MD and others. Obstetrics & Gynecology. 2010 Dec;116(6):1281-7.