IVF Mix-Up Couple Shares Update After Custody Agreement

Tiffany Score and Steven Mills -- the couple that gave birth to a baby who isn't theirs after an IVF mix-up in Florida -- are looking like a happy family ... at least in a new photo.

The couple shared a snap with their daughter, Shea ... holding her in their arms and kissing her cheeks.

Getting to this point was not easy ... as we reported, the biological parents only recently decided to give up custody to Tiffany and Steven, and were "heartbroken" over the agonizing decision.

However, Tiffany's family now says ... "The agreement came from a place of selfless love from all individuals ... Our family's hearts are filled with relief and gratitude."

Still, the couple says they're determined to find out how the IVF mix-up happened ... and they are seeking answers on their other viable embryos.