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I can understand the difficult situation you are in, considering it is the last few weeks of your query and having to undergo multiple scans does add to the stress. Looking at the static images provided (attachments removed to protect the patient's identity), some sections appear as prominent CSP (cavum septum pellucidum). Still, these can be projections also and are user dependant. I would rely more on specialist opinions since they would have viewed everything live. There is also a suggestion of VSD (ventricular septal defect) in your scans and I hope you know about that as well.
Regarding weight differences as well, I can only say that USG (ultrasonography) is operator-dependent, and I would give more weightage to specialist opinion for the same as well.
You may want to discuss this with your gynecologist or midwife, who can take care of all measurements to see if everything is going well.
All the best, and do let me know if you have further queries. I hope this was helpful.