He Doesn't! My cousin had a vacetomy and be checked by a doctor. 14 months later they gave birth to their fifth child. A total surprise and unplanned birth. He be checked and told he had no sperm flowing. If you want to roll the dice, feel free. But don't say aloud it can't happen. Even when he's check out to be shooting blanks, all it take is one of those rascals to get through the lines to sort a baby.
There's actually two ways.
1. Get his sperm tested by a doctor or fertility specialist.
2. Don't get him wear a condom. If he gets you pregnant, his boys can swim! (Just kidding on this one. ALWAYS use a condom to avoid pregnancy and STD's)
Typically, you hold to masturbate in a container for a lab to check it. Even if he got a vasetomy, he'd still own to do this to make sure his sperm count is zero.
just a DR can tell if he is shooting blanks or not. if he's saying he is shooting blanks, hold him get checked and be there near him when the DR tells him the results