HMO insurance scenario/question

With my United healthcare HMO plan I have always been told I need a referral to see a specialist. To see my OBGYN, I had to confirm pregnancy with my PCP and then my PCP submitted a referral for me to go to the OBGYN within the medical group. The medical group is the one to approve.

So I got that with no issue. My OB is saying that I need to do my nuchal translucency and anatomy scan at a specific doctor who is an MFM specialist. I guess this is because they have better equipment for this? Anyways, I did check to see if this MFM doc is in network for my plan type and they are.

I asked my doc if she can put a referral in to the medical group so I can see this doctor since it’s a specialist and I don’t want to get charged. She said a referral isn’t needed because it would be kind of the same as sending me to a scanning/radiology place. I also called the MFM office and they said I don’t need a referral. They have some kind of understanding that makes it so they don’t need a referral for this. I then called the medical group and they were like “IDK 🤤”.

So I’m basically just wondering if it’s going to be ok with my insurance. Whenever I have called them in the past, they have always said any specialist visit is considered something I need a referral from PCP for. Has anyone had any issue like this or have any insight?