Are they identical or not???

Since the very first ultrasound my dr told me she believed my twins were identical since they are sharing a placenta. They are each in their own sacs bc you can see the “separating membrane line” I believe is what she said. So I think they’re considered mono/di bc of this?? I received my results from genetic testing which was bloodwork that they sent someone to my home for & then submitted the results to me online. These results confirmed “two males, monozygotic/identical twins” ...but today at my 16wk ultrasound my dr said “I still believe they are identical but once they are born you can get them tested to make sure, if you care to confirm.” & I was like “I thought it was already confirmed through the genetic testing I already had bc my bloodwork said identical on there.” She was like “what really?? Are you sure?” ( she had previously told me that I would have to wait till after they were born to test ) but since my results came back confirming it already I’m like thinking “wth is going on here?” Lol but I have seen moms on here post though that they had to wait till after their babies were born to get them tested but what’s the reason for waiting? By choice or is it bc you were told you had to wait till after? I’m confused as to whether it is possible or not to confirm their “zygosity” through genetic testing while the babies are still in the womb? Bc if not then why do my results say that? Lol like did it used to be impossible & now it’s all of a sudden possible or??? Does anyone personally know from experience bc I’m so confused now.