Wa'alaikumassalam! At 12 weeks, EFW (estimated fetal weight) biasanya around 50-60 grams je, sangat kecil lagi so don't worry kalau sonogram tu susah nak detect or the measurement berapa-berapa, it's really hard to be accurate at this stage. Setiap baby grow differently so as long as doctor says okay, you're good! Kalau ada concerns memang better to ask the gynae directly, dia lagi boleh explain based on your scan, sebab masa 12 weeks ni margin of error boleh quite big.