If i had sex for the first time how soon could i get pregnant?

Anytime: Anytime you have sex without using birth control you could get pregnant. You have a 20-25% chance of getting pregnant each month in which you have had sex with no protection. If you are 'trying' to get pregnant, sometimes it takes a few months, even if everthing is perfectly normal.

Can not tell. : All that needs to happen is for a sperm to get to an egg. Even if a young woman has never menstruated, she might have just ovulated (released an egg) for the first time. This would make her fertile and pregnancy possible.