The transition phase is the final part of the first stage of labor, characterized by rapid and active cervical dilation from approximately 7 cm to a full 10 cm. This phase involves strong, frequent contractions that facilitate quick cervical effacement and dilation, preparing the cervix for the second stage. The latent phase involves slower dilation (<4 cm), while the expulsive and placental phases occur after full dilation. Therefore, the transition phase is key for active, rapid cervical dilation.

Reference: Williams Obstetrics, Cunningham et al., 25th Edition.