Hai mama! Congrats on 16 weeks, that's exciting! Honestly, timing boleh lah from 13-14 weeks onward kalau baby cooperate, tapi 16-17 weeks memang clearer la biasanya, depends heavily on baby's position, scan quality, and sonographer experience tu. A few of us tried to keep it surprise juga, and one of my mum friends managed until 20 weeks scan, but ya lor, some babies just "expose" themselves at routine scans haha, so your nurse is right, tak boleh guarantee 100%. If you're serious tentang surprise, boleh alert the sonographer beforehand and tutup mata jangan tengok screen, tapi some clinics kena inform diorang in advance so they can coordinate dengan radiologist. Either way, at 16 weeks dah boleh approach datang, so if you change your mind you can ask during your next scan!