Baby off scale sizewise-GD test

Nicola
Hi ladies I've just been into my 34 week midwife appt and both scan measurements and uterus measurements are indicating my baby is rapidly growing over previous 5 weeks. 
Some concerns by midwife today and they want to wait 3 weeks for the gestational diabetes test whereas I don't feel
Comfortable with that length of time. Contacted GP who is arranging via hospital for sooner fasting blood work and has worried me by saying my PCOS diagnosis is a risk factor and I should have been tested earlier!
I guess I'm wondering if anyone else has had their baby measuring off the scales in the third trimester and it NOT been gestational diabetes ??
Thanks