But the GD is pretty low on the intrusive scale - the sugar drink and a blood draw. GD can cause real problems in mom and baby, often shows up with no symptoms and the treatment is pretty low-impact - dietary changes, exercise and monitoring.
My OB is very naturally oriented (and a homeopath) and has not asked me to do the test in either of my pregnancies (no, you're not the only country that has the glucose test as part of routine prenatal testing!). Although I did not engage in a lengthy discussion with her about this (I totally wanted to avoid it, I find it very gross!) she told me briefly that the impact of such a sudden sugar rush to the fetus and the mother are yet unknown so it's better to exercise some caution and do not prescribe it unless there's a valid reason for it.
I think that if you make a search on Mothering's main web page you'd also find some information there by Dr. Buckley about the validity of this test.
By the way I highly recommend Dr Buckley's book to everyone who's expecting, it is one of the best and most thoughful books I've ever seen on natural birth, prenatal testing and early mothering choices.