Sir Elton John's partner David Furnish has said the couple want to have another child but "nothing's decided yet".
Furnish said he thought Zachary, born via a surrogate on Christmas Day 2010, "would be better" with a brother or sister.
He told the London Evening Standard: "It's something we talk about all the time. But in terms of when, where and how, nothing's decided yet."
Furnish said the couple would discuss it this summer and would like to go back to the same egg donor "so biologically there would...be a connection" to Zachary, but conceded she "has a life of her own".
He said: "It's a big commitment to make, nine months of their life that doesn't just affect them but their children, their husband, their partner".
The couple's civil partnership was formalised in 2005 and rock legend Sir Elton initially announced he wanted to adopt a 14-month-old boy from an orphanage in Ukraine.
But his plans to adopt were reportedly thwarted by Ukrainian laws.