Sayang, I understand you're worried, tapi please jangan stress dulu, okay. Since your doc dah check 4 times at 2 different clinics and everything else (head, body, arms) normal, the best thing is to have a proper discussion dengan your doctor about what this small measurement means for YOUR baby specifically, ada different reasons why, and they can monitor more closely moving forward. Try to take it one scan at a time, and if you're still anxious, ask your doctor for a referral to a specialist untuk peace of mind. You're doing great by getting checked regularly.
Nikkifiey Aziz