I did a research thread on I-T about this VERY TOPIC about 1.5 years ago, and had about 20 RESPONDEES who GOT their wives/gf's pregnant WHILE ON GEAR...

(and in that time I even got to see a girl impregnated FIRSTHAND while on a cycle...)
It will NEVER be used as a reliable SINGLE form of birth control in the USA...That I would bet my ENTIRE LIFE SAVINGS on...