Circus performers Hobbit Humphrey, 38, and Jake England-Johns, 35, appeared on BBC One's Inside Out last night.
They said they didn't even told baby Anoush's grandmother their baby's gender, but she found out when she changed their nappy at 11 months old.
The couple, from Bath, said their baby will decide its own pronoun and gender when it's older.
Speaking on the BBC programme, Mr England-Johns said: "Gender neutral refers to us trying to behave neutrally towards the child, rather than trying to make them neutral.
"We're not trying to make them be anything. We just want them to be themselves."
Hobbit Humphrey said: "So much of gender bias is unconscious. When I got pregnant we then were having a discussion about how we were going to mitigate the unconscious bias.
"And we figured that the only way we could do that was just not to tell people.
"To use the they/them pronoun for as long as we can, and create this little bubble for our baby to be who they are.
"Eventually they will get told by somebody that pink is only for girls and blue is only for boys, and you can't play with that because you are a particular sex.
"That's still a thing that happens these days. We're just trying to protect Anoush from that."
Mr Humprey's mum Camille, 64, said: "It was a struggle... but as with any learning over time it became embedded and they became 'they'."
Mr England-Johns added: "We are quite good now at holding space for people's discomfort in us saying, ''Actually, we don't tell anyone, we're not telling anyone for now''. We're just letting Anoush be a baby.
"Anoush is the most lovely little human. They're into everything, they're really active — just a delight."