Ah, ang transition sa 4 months is okay lang, pero mas importante talaga kung paano ang baby nyo mag-adjust sa new formula! Honestly, a few of us mums tried both Enfamil NAN Optipro at Nestogen, at ang feedback namin is na both are decent options, marami ring babies na umuunlatch well sa either one, pero may ilan na medyo may slight tummy adjustment muna. Personally, I'd suggest gradual mixing ng old at new milk para hindi ma-shock ang tummy ng baby, at observe kung paano siya mag-react sa unang week or two, some babies love it, some take time. If you notice any concerns like persistent constipation, rashes, or digestive issues after switching, better check with your pedia to make sure it's the right fit for your little one!