When to start pushing, and how
A Cochrane review and a large trial that disagree.
With an epidural, you can start pushing as soon as you are fully dilated, or wait an hour or so for the baby to descend on its own. The evidence points two ways and you should hear both.
Across 13 trials and 2,879 women, delayed pushing produced slightly more spontaneous vaginal births (relative risk 1.07), added about 56 minutes to the second stage, took about 19 minutes off actual pushing time, and roughly doubled the chance of a low cord pH at birth (relative risk 2.24).
A single much larger trial of 2,414 first-time mothers found no difference at all in spontaneous vaginal birth: 85.9% with immediate pushing against 86.5% with delayed. Immediate pushing shortened the second stage by 32 minutes and produced less chorioamnionitis (6.7% against 9.1%) and less postpartum hemorrhage (2.3% against 4.0%). Severe tearing was the same.
On directed versus spontaneous pushing, across 8 trials and 884 women there was no clear difference in tearing, episiotomy or spontaneous delivery rate. Being shouted at to hold your breath and count to ten has no demonstrated advantage over pushing how your body tells you to.