Walaupun tak common, tapi memang ada cases macam ni! Saya punya mum friend dulu scan awal cakap twins, then scan lagi dekat 12-13 minggu rupanya satu je, doc cakap mungkin one twin didn't develop or absorbed, it happens. Best thing is get another scan, maybe at a different clinic or with another doctor to confirm, sebab at 9 weeks timing pun boleh affect accuracy kena tengok positioning baby. Jangan stress dulu, just get it confirmed properly, doctor yang handle you akan explain what's going on, and either way, kamu ada support. Keep me posted if boleh, curious to know!