Final answer:
During the active phase of the first stage of labor, the cervix undergoes rapid dilation and effacement, typically dilating to 10 cm to allow for birth. This phase can last 6-12 hours but is highly variable and is facilitated by a positive feedback loop of uterine contractions.
Step-by-step explanation:
The expected rate of change of the cervix during the active phase of the first stage of labor is characterized by cervical dilation and effacement. Labor is often described as occurring in a positive feedback loop where uterine contractions help to stretch and dilate the cervix. This causes the cervix to thin, known medically as effacement. In the active phase of labor, contractions become more frequent and intense as the cervix dilates more rapidly, reaching up to 10 cm to allow for the passage of the baby.
For a vaginal birth to occur, full dilation of the cervix to 10 cm is necessary. The duration of this dilation stage can be quite variable, commonly taking 6-12 hours, but this can differ widely. Among factors like prior childbirths, each successive labor tends to involve shorter periods of cervical dilation.