Ahhh congrats on reaching 20 weeks! Honestly, at 20w5d the sonographer should be able to tell pretty accurately lah, tapi depends jugak on baby's position and how cooperative dia yang hari tu A few of my mum friends got their results confirmed at that scan and it was spot on, tapi one of them kena tell balik sebab baby was being shy! Best to ask the sonographer how confident they are with the reading, and then maybe do another quick scan around 24 weeks kalau you want double confirmation before you start the big shopping spree hehe.