Can you get pregnant from underwear with pre-ejaculate on it?

If the semen/pre-cum does not go at least into the vaginal opening for pregancy to have the chance to occur. Even with "thong" underware or a wedgie, the vaginal opening would never come in contact with the semen/cum/pre-cum. It also dies really fast unless it is kept at body temp. Even then, there studies show the sperm die quickly.

The semen/pre-cum needs to be at least as high as a tampon would go for a good chance for success. The higher you go the better the chance of pregnancy; the lower you go, the less likely you are to get pregnant.

Your underware doesn't even "get to the door"! This is no different than being afraid you will catch the flu by talking to a sick person on the phone.

Insufficient contact.