Active sperm test should clear this right up!

Hah! I was a vasectomy baby. Sorry about your luck, OP.

To be honest, I can't blame him. Get a paternity test and sue the place he got the vasectomy from.

Try taking him to a doctor to talk to him, or perhaps find some brochures at a place that does vasectomies? There has to be some kind of reliable information out there for you to show him. Maybe when you're getting a check up on the baby bring him along.

Send him to the doctor. One of my cousins was a post-vasectomy baby (they already had 4 kids and had decided that was plenty!) and they looked into it and yes, this does happen more often than you'd think. Good luck OP. Xx

There are things he can do to ease his mind if he suspects you've had an affair. He can go back to his urologist and have his ejaculate assessed for any viable sperm, which would show that his vasectomy reversed itself. If, in spite of knowing his vasectomy reversed, still accuses you of infidelity, then the only other thing you can do is have a paternity test completed once the baby is born. But I would like to assume that a test on his sperm would be proof enough for him to confirm that this child obviously is his. Keep your head up in the mean time...it'll be okay.

Prove it with a paternity test

if you've been faithful then the vasectomy failed and a DNA test later will prove that you were telling the truth my God even if you were cheating on him you wouldn't have unprotected sex send him back to the doctor to have his sperm tested again

Get him to do a sperm count check to prove your point

if after 8 to 9 months the body has failed to repair the damage, it gives up. Though this sounds exactly like how I came to be. This happened to my parents too.