Well I had a talk with the Obstetrician. As well as pointing out the risk factors I have - over 40, IVF baby, gestational diabetes - he also stated that the risk of me having a stillborn once the baby hits 39 weeks is pretty high. And he reiterated what Mel and Belfie have both said - because I am over 40, and have GD, the placenta may not be functioning as well as it could be. So there is absolutely no chance of him changing the date. So some straight talking and a little bit of a shock (again) really. I just hope now that baby stays ok.