I did not show with my first FOREVER. And I am bitty - 5'3", 100lbs prepregnancy, short torsoed, the whole deal. I was certain I would show IMMEDIATELY - and then I didn't! I was so disappointed. I was 28w before I "popped".
Now, with my 4th pregnancy, I pretty much show before I get a positive pregnancy test. And, I start out the same preprganancy weight. Plus, I've lost 6lbs due to hyperemisis - but the belly continues to grow.
This is me at 24w with my 1st.... hahaha, I'm bigger than that, NOW at 12w4d!

I know it is disheartening, I've totally been there!
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