Ay oo, mabago pa talaga especially kung early pa lang ang scan mo, around 12-16 weeks pa lang, mas mahirap makita ng malinaw kaya sometimes may mali. A few of us tried ulit ng scan around 18-20 weeks and iba na ang results, so it's really common! Best way is to confirm with your OB kung kailan mas accurate na makikita, usually by second trimester ultrasound na talaga ang clearer picture.