band like area in uterus at 15 weeks

So at my 12.5 week scan there was a band like area noted that was likely an amniochorionic separation but could be an amniotic band. I was asked to repeat an ultrasound in two weeks.

So I went at 15 weeks which was yesterday. The sonographer mentioned very confidently that she could still see the “amniotic band” but it’s small. I asked if it was around any organs she said no.

I’m in Canada so I’ll get my results from my dr next week right before I travel internationally for 2 weeks. I also will get my NIPT results then.

I am confused though because online it says that separation of membranes is normal until 16 weeks. So why did I need a repeat ultrasound before then? Is it not normal? I’m just worried that I’m travelling and won’t be able to get another scan till I’m 18.5 weeks. I read some studies that this could be a soft marker for chromosomal abnormalities or PROMM but again sooo many studies say it’s normal so I’m just confused why they keep flagging it in my ultrasound. I’ve had to have a million ultrasounds for several reasons and it’s just causing me anxiety.

I’m a STM mom fyi.