Alhamdulillah, at 31 weeks usually dah boleh confirm dengan quite accurate lah, especially kalau genitalia dia clear kat scan tu. A few of my mum friends yang scan late pregnancy memang accuracy nya tinggi, lagi-lagi kalau sonographer confident enough nak declare boy. Tapi jangan la berharap 100% jugak, sebab ada jugak rare cases position or shadow yang ttipu mata, so just keep an open heart and siap-siap je untuk surprise labour room! Which hospital you went to, usually the experienced sonographers boleh tahu betul.