I'd say get the size that corresponds with the size diaper you use. My DD1 is also 20 lbs - we use medium Super-Dos for her, and small ones for my 11-lb DD2.
I had two medium SuperDos, and I used them on my baby in RaRs with the fully unsnapped in the rise when she was about 3 mos old. I just sold them to another momma whose baby is about a 20 mos old.
We have larges (because the store was out of mediums) and my 22 lb DS has never even come close to saturating it. They don't fit in our FB OS though (well they do, but I can't get the legs tight enough with them in), but they fit great in our BG 4.0.
Re: ? re: superdo's
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