When do belly buttons typically pop out/go away?

Ke
I'm 18 weeks. I haven't gained any weight yet, but I'm already losing my belly button. I feel like this is so soon! The arrows in the picture are pointing to the holes of my former belly button piercing as a marker to show how much my belly is stretching out (because clearly the stretch marks weren't enough! Haha)
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For you moms who lost your belly button or had it pop out, when did it fully happen for you?