"Unable to obtain a 28 week scan"

I am very upset that my wife has not been booked in for her 28 week scan, which should have been this week 24/04/17 - 28/04/17. At the 20 week scan the sonographer was concerned about the position of the placenta, and as her BMI is slightly high she has been put on the consultancy lead route both of which I believe have stated that there should be a scan at 28 weeks. Today she has phoned to get an update and has been informed that the guidance has changed and a 30 week scan (despite having my reservations that this could be untrue) we are okay with this advice, but what boils my blood is that despite this only being 1.5 weeks to 2 weeks away still there is no appointment date/time provided, which means in another week we could conceivably find ourselves in the same boat. Scheduling appoints in maternity surely should be one of the easier functions in a hospital given it is not a surprise when the weeks are going to fall in the calendar and when scans/appointments are going to be required. We have both always worked and paid taxes for c.15 years, and "touch wood" we have not really required the NHS until now. I do have some sympathy that 2 sonographers are currently off work ill, but our baby is coming and my wife still needs the support and guidance she deserves. I hate complaining and I appreciate that pregnancy and births are just business as usual for yourselves, but this is our first, and rightly or wrongly not having confirmation of an appointment is causing my wife unnecessary stress, and as a helpless husband/father to be I am doing the only thing in my power and providing this feedback.