Answer:
Ignore the previous answer saying that vaginal fluids are acidic and cause sperm to die. If anything, the opposite is true. Vaginal fluids lubricate and also makes it easier for sperm to swim up to the egg.
Finally, it makes difference whether or not the man ejaculated before intercourse, so long as it doesn't affect sperm release during intercourse. Granted, chances may decrease slightly if the man cannot ejaculate, but remember that there is still "leakage" that can spill over to the uterus. But if the man still ejaculates during intercourse, it does not matter what happens before.