Well if each trial gives you a 30% chance, at 40 trials that gives you a 99.99993633% chance of success. If that's good enough odds for you, it should be enough. Those odds work unless there is something besides just bad luck working against you, such as slow sperm or low sperm counts.
Even if you bring the chance down to 5% each trial, at 40 trials that still gives you about a 87% chance.