Can a pre-conception parentage agreement be challenged after the child is born?

A pre-conception parentage agreement can be challenged, but it is not simply set aside because someone changes their mind — Ontario courts treat these agreements as strong evidence of what the parties intended, and generally give effect to them where they were properly made, with independent legal advice, and the parties' conduct after the birth is consistent with the agreement. A challenge is more likely to succeed where the agreement was signed without independent legal advice, where it doesn't meet the legislation's basic requirements, such as being made before conception, or where there's evidence a party didn't genuinely understand or agree to its terms.

In some situations — most notably where a surrogate does not provide the written post-birth confirmation the automatic route depends on — the agreement alone cannot finalize parentage, and the matter has to go to court for a declaration of parentage regardless of what the agreement says. Anyone facing a dispute over a parentage agreement should get legal advice quickly, since the strength of the original paperwork will shape what a court is willing to do.