I believe this deep-breath exercising helps labor two ways. One, it makes key muscles stronger. Two, it trains me to focus.
Just one squat tells me that my thigh muscles aren't in any shape for delivering in the classic squat position. By the way, Kegel exercises are also important for pelvic floor muscles.
The anchoring breaths of yoga prepare me to focus during contractions. Focus feels impossible when the waves crash over me. I have to train to relax under that much pressure.
How do you train for labor and delivery?
More info? Fit to be Pregnant offers a training plan.