Alah, 266g pada 18 minggu tu normal je, sayang! Biasanya janin pada minggu ke-18 memang seberat tu, some babies are slightly heavier or lighter tapi still dalam range yang healthy. A few of my mum friends had similar readings and their babies turned out perfectly fine, so jangan worry sangat. If you're concerned though, boleh je tanya ultrasound technician or your doc during the next visit, they'll confirm everything's progressing well based on your whole scan, bukan hanya berat je.