As far as nature us concerned, the purpose of intercourse is pregnancy, so the odds are stacked seriously on favour of pregnancy as a result of pregnancy.
As Buenchco says, you can reduce the odds, but not eliminate them by the method you are using.
Remember, if every sperm fertilised an egg, you would repopulate the continent of North America - that's the level of odds in the risk you are taking.
As the old saying has it - what do you call couples who use the withdrawal method?
Parents!
As a point of interest, why can't your partner use a condom?