Bittersweet Ending: The baby Changeling dies, but it merges with Odo and restores his powers. The O'Briens' new baby is born, but Kira is saddened to not have a child of her own to hold.
Both Sides Have a Point: Both Odo and Mora Pol ultimately are shown to have points in their arguments regarding raising the changeling. Eventually they do resort to Mora's more painful techniques, which finally get the baby changeling to alter its shape...but then it attempts to mimic Odo's face, showing that the more nurturing approach Odo had used earlier hadn't been totally wasted.
O.O.C. Is Serious Business: Quark is suspicious of Odo being chummy with him, as it usually means that Odo wants something from him, usually a confession. It takes him a while to accept that Odo, for once, is genuinely happy.
Open-Minded Parent/Education Mama: Odo and Mora basically become this. Odo, the open-minded one who doesn't want to push his baby blob too hard. And Mora, the guy who'd rather use tests to get the baby moving.
Mora Pol: If it wasn't for me, you'd still be sitting on a shelf somewhere in a beaker labeled 'unknown sample'. Odo: If it wasn't for me, you'd be a nobody. Starfleet wouldn't hire you to judge a science fair!
Yank the Dog's Chain: For once in his life, raising the baby Changeling has made Odo is truly, genuinely happy - naturally, it dies. Best summed up in the way The Reveal takes place: Odo goes on a long, cheerful monologue to Quark about how connecting to the Changeling has not only made him feel better, but finally made him reconnect to what its like to be a Changeling and made his life as a solid seem not so bad... and then he immediately gets the call that the Changeling is dying.