Basically there is no agreement across relevant national and international health bodies around threshold numbers and even testing criteria. As many in this thread have noticed, the way the GTT/OGTT test is administered, the instructions around fasting beforehand, and the timing of the test all varies widely.
For example, these are the different threshold numbers various relevant agencies use for GD diagnosis (and to some extent, target glucose range):
World Health Organization:
Fasting - 7.0 mmo/l (126mg/dl)
2 Hour post prandial - 7.8 mmo/l (140mg/dl)
American Diabetes Association:
Fasting - 5.3 mmo/l (95mg/dl)
1 Hour post prandial - 10.0 mmo/l (180mg/dl)
2 Hour post prandial - 8.6 mmo/l (155 mg//dl)
The National Diabetes Data Group:
Fasting - 5.8 mmo/l (105mg/dl)
1 Hour post prandial - 10.6 mmo/l (190mg/dl)
2 HOur post prandial - 9.2 mmo/l (165 mg/dl)
International Association of Diabetes in Pregnancy Group (IADPSG):
FAsting - 5.1 mmo/l(95 mg/dl)
1 HOur post prandial - 10.0mmo/l (180mg/dl)
2 Hour post prandial - 8.5 mmo/l (153 mg/dl)
The IADPSG threshold is what Canada has moved towards using over the past 2 years. Essentially though, there is NO consensus on diagnostic criteria and threshold numbers from one country (or sometimes even clinician) to the next.
In terms of target glucose numbers, some endocrinologists seem to recommend target numbers more in line with Type 2, non pregnancy diabetes - under 6.0 fasting, and under 8.0 2 hours post prandial. Most doctors seem to gravitate towards getting women into the range of the average glucose in pregnancy numbers that were discerned during the HAPO study (i've mentioned this study before, it looked at the average glucose numbers of over 25,000 women during pregnancy):
Fasting - 70-80mmol/3.9-4.4 mg/dl
1 hour after meal - 110-120mmol/6.1-6.7 mg/dl
2 hours after meal - 100-110mmol/5.5-6.1 mg/dl
There also seems to be a lack of consensus around which numbers to be more concerned about - fasting or 1-2 hour post prandial. In terms of post prandial numbers, some docs seem more concerned about how high you spike (1 hour number) versus your body's ability to control and decline from the spike (2 hour). It seems as though the biggest concern may be long term high blood glucose levels, which is why there is more concern with the 2 hour number in general (our BG rises within about 15 mins of eating and spikes after about 45 mins - so if it is still really high 2 hours later, that is very suggestive). So basically, there is a lot of fuzziness still around diagnosis and the target glucose range women should be aiming for during pregnancy. This should be *somewhat* reassuring though - there is no hard, definitive line where excessive glucose translates into a concrete negative outcome. Interestingly, I also noted (because I ended up with two blood glucose monitors) even the numbers we are finding during our tests can be off - my numbers were often as much as 1 mmo/l off between machines, and it wasn't always the same one giving the high number. When I asked the GD nurse if I could test my own numbers with the machines postpartum she said no....because the numbers they produce "are not reliable"
Anyways, I hope that info helps!
! Anyway, my point is it's all subjective until you get that baby out in the world and on a set of scales.
