Does peeing before intercourse eliminate sperm in pre-ejaculate?

Not likely: No. Urine is acidic so it might have a minor effect on the sperm

It would cut it down: It's NOT a good birth control method. It's merely a reduction in the probability of conception. If there was any recent flow of sperm (masturbation, etc) most will wash away w/ urine, but no guarantee for all. If you've missed a period, do a test and in the future use real protection. For pregnancy AND STDs. It's smart and caring. And that's sexy.