Not that this is a reason to attend childbirth class, but did you happen to read the news article about the NY subway conductor who assisted a mother in labor?
The emerging newborn slid right into her (the conductor's) hands.
A concerned by-stander kept the crowd down and away from the mother, who birthed her baby in about 7 minutes after her water broke.
Oh, and the mother was sitting on the seat of the subway - naturally using the upright and gravity positive position for birth!
You can read more here.
And see the interview with the conductor, here!