Protracted disorders refer to a series of events including protracted active phase dilation (slower than normal rate of cervical dilation) and protracted descent (delayed descent of the fetal head in the active phase). A laboring woman, who has a slower than normal rate of cervical dilation, is said to have a protraction disorder. Diagnostic criteria are 1.2 cm per hour for primips and 1.5 cm per hour for multips. For protracted descent, the criteria are less than 1.0 cm per hour in primips and less than 2.0 cm per hour for multips.
A slow progress may be the result of CPD or cephalopelvic disproportion . Most women, however, benefit greatly from adequate hydration and some nutrition, emotional reassurance, position changes ~ these women may go on and deliver vaginally.
Arrest disorders include secondary arrest of dilation (no progress in cervical dilation in more than 2 hours), arrest of descent (fetal head does not descend for more than 1 hour in primip and more than 0.5 hours in multip), and failure of descent (no descent).
Much of the diagnostic reference for protracted disorders is associated with the Friedman Labor Curve. For the past half-century obstetric practice has followed the description of normal labor set out in a landmark, 500 person study by Dr. Emanuel Friedman.
Friedman established the following definitions of labor progression in 1955:
* Protracted active labor: less than 1.2 cm/hr.
* Active phase at rest: no dilation for 2 hours.
* Protracted descent: less than 1 cm/hr.
* Arrested descent: no descent for 1 hour.
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.
Generally, when there is a plateau (stopping of progress) of two hours in Friedman's curve while in a non-medicated active labor, or of three hours in active labor with an epidural, then "failure to progress" is the diagnosis and C-section is indicated. Of course, evaluation of the "4 Ps" -- Power, Psyche, Passenger, and Passageway (basically this means the force of labor, mental preparedness of the mother, the size and position of the baby, and the size of the birth canal) must be made to see if there is a correctable measure.
Resources for education:
Definitions of labor protraction, arrest challenged. (Reassessment of Friedman Curve). OB/GYN News, March 1, 2002, by Nancy Walsh.
Reeder, S., Martin, L., and Koniak-Griffin, D. Maternity Nursing: Family, Newborn, and Women's Health Care. (1997) Philadelphia: J.B. Lippincott Company.
Varney, H., Kriebs, J., and Gegor, C. Varney's Midwifery: 4th Edition. Jones and Bartlett Publishers. Sudbury, Massachusetts. 2004.
Zhang J, Troendle J.F., Yancey M.K. Reassessing the Labor Curve in Nulliparous Women American Journal of Obstetrics and Gynecology. 2002;187(4):824-828.