The second stage of labor begins with full cervical dilation and ends with the delivery of the baby. A key clinical sign indicating progression into this stage is the urge to push, which results from the fetal head descending and stimulating the pelvic floor and rectal nerves. This sensation prompts the mother to actively participate in the delivery process. Other options such as onset of contractions, cervical effacement, and loss of mucus plug occur earlier in labor, primarily in the first stage. Recognizing the urge to push allows timely guidance and support for effective maternal effort during delivery.

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