BHL was away for my 19 week scans aswell, you can ring and ask them but I think they like it at 19 weeks as they then do all the test that need to be done ( this takes awhile ) If they tell you they want you in at 19 weeks just ask if you can book another appointment when you DH is home this is what I always did and they were fine with it, but most the time you will need to go to your GP to get another refural ( sp?)