Hi,
My pre pregnancy ratio was 1:10 which moved to 1:8 from weeks 16 to 34. Then from week 34 to 37+3 it was 1:6. So it didn't change drastically until the last few weeks. My basal insulin doubled though and I changed from one injection at night to splitting my daily dose in half and injecting 12 hours apart (10am and 10pm).
Hope this helps!