Definitions of labor protraction, arrest challenged. (Reassessment of Friedman Curve).

NEW ORLEANS -- Current definitions of labor protraction and arrest may be too stringent, Dr. Jun Zhang said at the 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 of the National Institute of Child Health and Human Development, Bethesda, Md.

For the past half-century obstetric practice has followed the description of normal labor set out in a landmark 1955 study by Dr. Emanuel Friedman. Based on his observations of 500 women, Dr. Friedman divided labor into four phases: latent, acceleration, maximum slope, and deceleration.

He also established a series of definitions commonly used to this day. (See box.)

From his data he derived a curve that bears his name predicting the normal course of labor, charting hours of labor against dilation of the cervix measured in centimeters.

But this curve has never undergone rigorous testing, and much has changed in the last half century, Dr. Zhang said. There have been changes in obstetric practice such as the increased use of epidural anesthesia and oxytocin and the decreased use of forceps.

Maternal and fetal weights also have increased.