Missing Cisterna Magna

Lo

Hey all - On our last ultrasound of one of our babies, (we are expecting triplets) she is measuring about 14-16 days behind and they said they couldn’t find the cisterna magna in her brain. I was 18+5 at that scan - im 19+3 today. Has anyone gone through this?? They didn’t really tell us much and we had no clue what questions to ask.....