Congratulations sa normal CAS results, mama! That's the main thing na importante talaga, and if your OB-sono already assured you it's nothing to worry about, I'd trust that kasi sila ang nakakita ng actual ultrasound. One of my mum friends had a similar finding din with her first baby, slightly larger measurement sa isang part, and the doctor explained it's just normal variation na nangyayari, honestly hindi naman big deal sa grand scheme of things. The fact na everything else is normal and your doctor gave you peace of mind is what matters most; if you're still feeling anxious about it though, feel free to ask your OB ulit sa next visit just para sa your own peace of mind, pero from what you're sharing, sounds like your baby's doing just fine!