The 1 cm an hour rule is dead, and people still quote it
Both bodies that taught the rule have formally dropped it, and one of the documents most often quoted at women has been withdrawn from circulation.
If you have been told to expect about a centimeter an hour, you have been given a number from studies of women who labored in the 1950s.
Emanuel Friedman drew the original curves, in one paper on first labors in 1955 and one on later labors in 1956. His criteria, as the modern American researchers restate them, called active labor abnormal if the cervix opened slower than 1.2 cm an hour in a first labor or slower than 1.5 cm an hour in a later one.
ACOG's own current guideline describes them like this: Using these data, the 95th percentile of latent phase duration was 20 hours in nulliparous patients and 14 hours in multiparous patients. The transition from latent to active phase was thought to occur at approximately 4 cm cervical dilation. Friedman observed that the 95th percentile rate of active phase cervical dilation ranged from 1.2 cm/hour in nulliparous patients to 1.5 cm/hour in multiparous patients.
Read that carefully: 1.2 and 1.5 are the slowest normal rates in Friedman's data, not the expected ones. The rule was always a floor, and it turned into a target.
WHO has formally recommended against it. Two recommendations, in WHO's own words, both filed under Not Recommended:
For pregnant women with spontaneous labour onset, the cervical dilatation rate threshold of 1 cm/hour during active first stage (as depicted by the partograph alert line) is inaccurate to identify women at risk of adverse birth outcomes and is therefore not recommended for this purpose.
A minimum cervical dilatation rate of 1 cm/hour throughout active first stage of labour is unrealistically fast for some women and is therefore not recommended for identification of normal labour progression. A slower than 1-cm/hour cervical dilatation rate alone should not be an indication for obstetric intervention.
And WHO says why it matters: The GDG acknowledged that in hospital settings the use of the alert line and attempts to maintain cervical dilatation progression of 1 cm/hour lead to unnecessary interventions due to the perception that labour progress is pathologically slow.
ACOG moved the starting line instead. Its current guideline says: ACOG recommends that cervical dilation of 6 cm be considered the start of the active phase of labor.
That replaced the old 4 cm threshold. And the sentence that changes what failure to progress means: Thus, a slow but progressive active phase of labor demonstrating cervical change at least every 4 hours in the setting of reassuring maternal and fetal status should not be an indication for cesarean delivery.
Withdrawn Clinical Document. It was replaced in January 2024 by Clinical Practice Guideline No. 8, whose own header reads
Number 8 (Replaces Obstetric Care Consensus 1, March 2014). A correction to Guideline No. 8 was published in March 2025. This guide could not obtain the text of that correction, so nothing here is asserted to be free of it.
One more piece of honesty, from ACOG itself, about whether any of these changes helped: Thus, the true effect of the 2014 changes in ACOG definitions and guidance for management of labor arrest remains unclear, particularly regarding maternal and neonatal morbidity. However, these suggestions provide a general framework for clinicians to reasonably balance the risks of prolonged labor with the potential benefit of avoiding cesarean delivery, with room for individualization.
That is a guideline saying its own effect on outcomes is unknown. It is worth knowing that it says so.
"Is that the 2024 guideline, or the 2014 one that was withdrawn?"
"Is anything worrying you about me or the baby right now, apart from the clock?"