Reddit user Throwawaymyspermazoa opened up to the internet about his dilemma.
Late last year the couple decided to try for kids. The pair were hit with bad news: he was completely infertile without surgery.
"I was diagnosed with azoospermia last December," he told readers.
"Blockage in the pipes just meant I wasn't actually producing any sperm when ejaculating.
"It's curable with surgery thankfully, and we finally got it scheduled this July."
But five months later, before having surgery, there was an interesting change of events: she fell pregnant.
"She took three tests though, and sure enough they're all positive."
In the past, he says he's had unfaithful partners. And given the doctor's word, he immediately feared the worst: this baby wasn't his.
"I'm not the jealous type, but I'm literally stuck. The doctors said this couldn't happen. And I can't believe my wife would jeopardise the future we've been so excited for over some fling when we seem to have such a great emotional and physical connection," he continued.
"My wife's been ecstatic. She's given no indication of any guilt or worry that she may have cheated. She was so excited when she first found out that I didn't express my worries then. But she left for work and now I feel completely torn. What if she did cheat?"
The thought that he was a soon-to-father to someone else's kid continued to irritate him. Different scenarios played out in his head that could offer an explanation.
"Looking back now there's a few tiny things that didn't seem to be an issue but now have me wracking my brain for clues.
"Her job often has her taking clients out for dinner and it's not uncommon for her to get back later in the evening.
"She definitely had a busy last few months, but that's not uncommon for her job.
He also noticed some other out-of-character signs.
"She always wears one of the same two perfumes, but she came back one night smelling completely different.
"I remember seeing a text message on her lock screen of just a winky face, a different time, but assumed it was one of her girlfriends."
He set up a doctor's appointment that would either confirm his suspicions or find out if this miracle baby was actually his.
While he waited, he turned to his friends on the internet. The crowd of commenters were supportive, suggesting that there could easily be a possibility it was his.
"My friend had [a] vasectomy. He went for checkups was told no sperm," one user replied.
"Then about a year later his wife gets pregnant. There is no doubt it is his. It looks just like him.
"I know this is [a] different situation but you never know. Doctors are wrong sometimes.
"I know plenty of women too who were told they couldn't get pregnant by doctors due to infertility issues and then they got pregnant naturally unexpectedly."
Another offered a more scientific explanation: "I literally just studied this! OK, so although you’ve been diagnosed with azoospermia it means that when they looked at your semen in the lab it didn’t have any sperm in it.
"However, you produce a lot of semen and the lab only looks at a tiny fraction of it which usually gives a good response.
"Usually you would repeat several times before concluding it's azoospermia, although just because the lab didn’t see any sperm it can just mean that you had an incredibly low count so none of their samples from the sample you have showed any."
In his latest update, Throwawaymyspermazoa mentions that his wife has (conveniently) booked an appointment at a time when he can't go. The two have planned to have a chat when they both get back from work. Meanwhile, he's also getting a second urology opinion to confirm his fertility status.