From the beginning of labor to the full opening (dilation) of the cervix—to about 4 inches (10 centimeters).
Contractions are irregular at first but become progressively stronger and more rhythmic.
The cervix begins to thin and opens to about 1 1/2 inches (4 centimeters).
The initial phase lasts an average of 8 hours (usually no more than 20 hours) in a first pregnancy and 5 hours (usually no more than 12 hours) in subsequent pregnancies.
The cervix opens from about 1 1/2inches (4 centimeters) to the full 4 inches (10 centimeters). It thins and pulls back (effaces) until it merges with the rest of the uterus.
The presenting part of the baby, usually the head, begins to descend into the woman’s pelvis.
The woman begins to feel the urge to push as the baby descends, but she should resist it. Pushing too early may be unnecessarily tiring and frequently tears the cervix, which then must be repaired.
This phase averages about 5 to 7 hours in a first pregnancy and 2 to 4 hours in subsequent pregnancies.
From the complete opening of the cervix to delivery of the baby: This stage usually lasts about 2 hours in a first pregnancy and about 1 hour in subsequent pregnancies. It may last another hour or more if the woman has been given an epidural injection or a drug to relieve pain. During this stage, the woman pushes.
From delivery of the baby to delivery of the placenta: This stage usually lasts only a few minutes but may last up to 30 minutes.