Is there a theory about showing early could u guess the sex of baby just by the bump

Hi ladies I'm 13weeks 4 days I'm wondering if there any miths or theory's bout showing early and can that give sex of the baby away ? Can anyone guess for little bit of fun all my friends says I'm starting to get a bump but I'm not sure Iv already got daughter but I didn't really show with her until I was round 20weeks,